mod(event): do not care about enum declarations

The union type can not be constructed with declarations anyway:
`error: reified unions must have no decls`; meaning there is no point in
even trying to do so.

README.md

@@ -2,7 +2,7 @@
 
 `zterm` is a terminal user interface library (*tui*) to implement terminal (fullscreen or inline) applications.
 
-> [!CAUTION]
+> [!caution]
 > Only builds using the zig master version are tested to work.
 
 ## Demo
@@ -13,7 +13,7 @@ Clone this repository and run `zig build --help` to see the available examples.
 zig build --release=safe -Dexample=demo run
 ```
 
-> [!TIP]
+> [!tip]
 > Every example application can be quit using `ctrl+c`.
 
 See the [wiki](https://gitea.yves-biener.de/yves-biener/zterm/wiki) for a showcase of the examples and the further details.

build.zig

@@ -11,7 +11,9 @@ pub fn build(b: *std.Build) void {
         button,
         input,
         progress,
+        radio_button,
         scrollable,
+        selection,
         // layouts:
         vertical,
         horizontal,
@@ -33,20 +35,15 @@ pub fn build(b: *std.Build) void {
     options.addOption(bool, "debug", debug_rendering);
     const options_module = options.createModule();
 
-    // dependencies
-    const zg = b.dependency("zg", .{
-        .target = target,
-        .optimize = optimize,
-    });
-
     // library
     const lib = b.addModule("zterm", .{
         .root_source_file = b.path("src/root.zig"),
         .target = target,
         .optimize = optimize,
+        .imports = &.{
+            .{ .name = "build_options", .module = options_module },
+        },
     });
-    lib.addImport("code_point", zg.module("code_point"));
-    lib.addImport("build_options", options_module);
 
     //--- Examples ---
     const examples = std.meta.fields(Examples);
@@ -54,45 +51,52 @@ pub fn build(b: *std.Build) void {
         if (@as(Examples, @enumFromInt(e.value)) == .all) continue; // skip `.all` entry
         const demo = b.addExecutable(.{
             .name = e.name,
-            .root_source_file = b.path(switch (@as(Examples, @enumFromInt(e.value))) {
-                .demo => "examples/demo.zig",
-                .continuous => "examples/continuous.zig",
-                // elements:
-                .alignment => "examples/elements/alignment.zig",
-                .button => "examples/elements/button.zig",
-                .input => "examples/elements/input.zig",
-                .progress => "examples/elements/progress.zig",
-                .scrollable => "examples/elements/scrollable.zig",
-                // layouts:
-                .vertical => "examples/layouts/vertical.zig",
-                .horizontal => "examples/layouts/horizontal.zig",
-                .grid => "examples/layouts/grid.zig",
-                .mixed => "examples/layouts/mixed.zig",
-                // styles:
-                .text => "examples/styles/text.zig",
-                .palette => "examples/styles/palette.zig",
-                // error handling
-                .errors => "examples/errors.zig",
-                .all => unreachable, // should never happen
+            .root_module = b.createModule(.{
+                .root_source_file = b.path(switch (@as(Examples, @enumFromInt(e.value))) {
+                    .demo => "examples/demo.zig",
+                    .continuous => "examples/continuous.zig",
+                    // elements:
+                    .alignment => "examples/elements/alignment.zig",
+                    .button => "examples/elements/button.zig",
+                    .input => "examples/elements/input.zig",
+                    .progress => "examples/elements/progress.zig",
+                    .radio_button => "examples/elements/radio-button.zig",
+                    .scrollable => "examples/elements/scrollable.zig",
+                    .selection => "examples/elements/selection.zig",
+                    // layouts:
+                    .vertical => "examples/layouts/vertical.zig",
+                    .horizontal => "examples/layouts/horizontal.zig",
+                    .grid => "examples/layouts/grid.zig",
+                    .mixed => "examples/layouts/mixed.zig",
+                    // styles:
+                    .text => "examples/styles/text.zig",
+                    .palette => "examples/styles/palette.zig",
+                    // error handling
+                    .errors => "examples/errors.zig",
+                    .all => unreachable, // should never happen
+                }),
+                .target = target,
+                .optimize = optimize,
+                .imports = &.{
+                    .{ .name = "zterm", .module = lib },
+                },
             }),
-            .target = target,
-            .optimize = optimize,
         });
-        // import dependencies
-        demo.root_module.addImport("zterm", lib);
         // mapping of user selected example to compile step
         if (@intFromEnum(example) == e.value or example == .all) b.installArtifact(demo);
     }
 
     // zig build test
     const lib_unit_tests = b.addTest(.{
-        .root_source_file = b.path("src/root.zig"),
-        .target = target,
-        .optimize = optimize,
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/root.zig"),
+            .target = target,
+            .optimize = optimize,
+            .imports = &.{
+                .{ .name = "build_options", .module = options_module },
+            },
+        }),
     });
-    lib_unit_tests.root_module.addImport("code_point", zg.module("code_point"));
-    lib_unit_tests.root_module.addImport("DisplayWidth", zg.module("DisplayWidth"));
-    lib_unit_tests.root_module.addImport("build_options", options_module);
 
     const run_lib_unit_tests = b.addRunArtifact(lib_unit_tests);
 

build.zig.zon

@@ -35,12 +35,7 @@
     // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
     // Once all dependencies are fetched, `zig build` no longer requires
     // internet connectivity.
-    .dependencies = .{
-        .zg = .{
-            .url = "git+https://codeberg.org/atman/zg#9427a9e53aaa29ee071f4dcb35b809a699d75aa9",
-            .hash = "zg-0.14.1-oGqU3IQ_tALZIiBN026_NTaPJqU-Upm8P_C7QED2Rzm8",
-        },
-    },
+    .dependencies = .{},
     .paths = .{
         "LICENSE",
         "build.zig",

examples/continuous.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -41,7 +41,7 @@ const Spinner = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -57,18 +57,20 @@ const Spinner = struct {
 };
 
 const InputField = struct {
+    allocator: std.mem.Allocator,
     input: std.ArrayList(u21),
     queue: *App.Queue,
 
     pub fn init(allocator: std.mem.Allocator, queue: *App.Queue) @This() {
         return .{
-            .input = .init(allocator),
+            .allocator = allocator,
+            .input = std.ArrayList(u21).initCapacity(allocator, 8) catch unreachable,
             .queue = queue,
         };
     }
 
-    pub fn deinit(this: @This()) void {
-        this.input.deinit();
+    pub fn deinit(this: *@This()) void {
+        this.input.deinit(this.allocator);
     }
 
     pub fn element(this: *@This()) App.Element {
@@ -81,14 +83,14 @@ const InputField = struct {
         };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
             .key => |key| {
-                if (key.isAscii()) try this.input.append(key.cp);
+                if (key.isAscii()) try this.input.append(this.allocator, key.cp);
 
                 if (key.eql(.{ .cp = zterm.input.Enter }) or key.eql(.{ .cp = zterm.input.KpEnter }))
-                    this.queue.push(.{ .accept = try this.input.toOwnedSlice() });
+                    this.queue.push(.{ .accept = try this.input.toOwnedSlice(this.allocator) });
 
                 if (key.eql(.{ .cp = zterm.input.Backspace }))
                     _ = this.input.pop();
@@ -100,7 +102,7 @@ const InputField = struct {
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -131,7 +133,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -176,7 +178,7 @@ pub fn main() !void {
         if (now_ms >= next_frame_ms) {
             next_frame_ms = now_ms + tick_ms;
         } else {
-            time.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
+            std.Thread.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
             next_frame_ms += tick_ms;
         }
 
@@ -212,7 +214,7 @@ pub fn main() !void {
                 else => {},
             }
 
-            container.handle(event) catch |err| app.postEvent(.{
+            container.handle(&app.model, event) catch |err| app.postEvent(.{
                 .err = .{
                     .err = err,
                     .msg = "Container Event handling failed",
@@ -228,7 +230,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -240,6 +242,6 @@ const std = @import("std");
 const time = std.time;
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {
+const App = zterm.App(struct {}, union(enum) {
     accept: []u21,
 });

examples/demo.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    pub fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    pub fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -33,7 +33,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -168,7 +168,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -183,7 +183,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -195,4 +195,4 @@ const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
 const input = zterm.input;
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/alignment.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -32,7 +32,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -70,7 +70,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -85,7 +85,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -96,4 +96,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/button.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -40,7 +40,7 @@ const Clickable = struct {
         };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
             .mouse => |mouse| if (mouse.button == .left and mouse.kind == .release) {
@@ -55,7 +55,7 @@ const Clickable = struct {
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -82,7 +82,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -119,7 +119,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -134,7 +134,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -145,7 +145,10 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {
-    click: [:0]const u8,
-    accept,
-});
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        click: [:0]const u8,
+        accept,
+    },
+);

examples/elements/input.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -37,7 +37,7 @@ const MouseDraw = struct {
         };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
             .mouse => |mouse| this.position = .{ .x = mouse.x, .y = mouse.y },
@@ -45,7 +45,7 @@ const MouseDraw = struct {
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
         const this: *@This() = @ptrCast(@alignCast(ctx));
 
@@ -65,7 +65,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -133,7 +133,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -148,7 +148,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -161,6 +161,9 @@ const assert = std.debug.assert;
 const zterm = @import("zterm");
 const Color = zterm.Color;
 
-const App = zterm.App(union(enum) {
-    accept: []u8,
-});
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        accept: []u8,
+    },
+);

examples/elements/progress.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -32,25 +32,59 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
     var progress_percent: u8 = 0;
-    var progress: App.Progress(.progress) = .init(&app.queue, .{
-        .percent = .{ .enabled = true },
-        .fg = .green,
-        .bg = .grey,
-    });
     var quit_text: QuitText = .{};
 
     var container = try App.Container.init(allocator, .{
-        .layout = .{ .padding = .all(5) },
+        .layout = .{ .padding = .all(5), .direction = .vertical },
     }, quit_text.element());
     defer container.deinit();
 
-    try container.append(try App.Container.init(allocator, .{}, progress.element()));
-
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .left,
+            },
+            .fg = .blue,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .middle, // default
+            },
+            .fg = .red,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{
+                .enabled = true,
+                .alignment = .right,
+            },
+            .fg = .green,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
+    {
+        var progress: App.Progress(.progress) = .init(&app.queue, .{
+            .percent = .{ .enabled = false },
+            .fg = .default,
+            .bg = .grey,
+        });
+        try container.append(try App.Container.init(allocator, .{}, progress.element()));
+    }
     try app.start();
     defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
 
@@ -67,7 +101,7 @@ pub fn main() !void {
         if (now_ms >= next_frame_ms) {
             next_frame_ms = now_ms + tick_ms;
         } else {
-            time.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
+            std.Thread.sleep((next_frame_ms - now_ms) * time.ns_per_ms);
             next_frame_ms += tick_ms;
         }
 
@@ -104,7 +138,7 @@ pub fn main() !void {
                 else => {},
             }
 
-            container.handle(event) catch |err| app.postEvent(.{
+            container.handle(&app.model, event) catch |err| app.postEvent(.{
                 .err = .{
                     .err = err,
                     .msg = "Container Event handling failed",
@@ -120,7 +154,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -132,6 +166,9 @@ const std = @import("std");
 const time = std.time;
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {
-    progress: u8,
-});
+const App = zterm.App(
+    struct {},
+    union(enum) {
+        progress: u8,
+    },
+);

examples/elements/radio-button.zig

@@ -0,0 +1,98 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var radiobutton: App.RadioButton = .init(false, .{
+        .label = "Test Radio Button",
+        .style = .squared,
+    });
+    var button: App.Button(.accept) = .init(&app.queue, .init(.default, "Button"));
+    var quit_text: QuitText = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .grey },
+        .layout = .{ .padding = .all(5) },
+    }, quit_text.element());
+    defer container.deinit();
+    try container.append(try .init(allocator, .{}, radiobutton.element()));
+    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .black } }, button.element()));
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        // pre event handling
+        switch (event) {
+            .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
+            .accept => log.info("Clicked built-in button using the mouse", .{}),
+            .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+            else => {},
+        }
+
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
+            .err = .{
+                .err = err,
+                .msg = "Container Event handling failed",
+            },
+        });
+
+        // post event handling
+        switch (event) {
+            .quit => break,
+            else => {},
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const App = zterm.App(struct {}, union(enum) {
+    accept,
+});

examples/elements/scrollable.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -34,7 +34,7 @@ const HelloWorldText = packed struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -66,7 +66,7 @@ pub fn main() !void {
     }
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -169,7 +169,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -184,7 +184,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -196,4 +196,4 @@ const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
 const input = zterm.input;
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/elements/selection.zig

@@ -0,0 +1,97 @@
+const QuitText = struct {
+    const text = "Press ctrl+c to quit.";
+
+    pub fn element(this: *@This()) App.Element {
+        return .{ .ptr = this, .vtable = &.{ .content = content } };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
+        _ = ctx;
+        assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
+
+        const row = 2;
+        const col = size.x / 2 -| (text.len / 2);
+        const anchor = (row * size.x) + col;
+
+        for (text, 0..) |cp, idx| {
+            cells[anchor + idx].style.fg = .white;
+            cells[anchor + idx].style.bg = .black;
+            cells[anchor + idx].cp = cp;
+
+            // NOTE do not write over the contents of this `Container`'s `Size`
+            if (anchor + idx == cells.len - 1) break;
+        }
+    }
+};
+
+pub fn main() !void {
+    errdefer |err| log.err("Application Error: {any}", .{err});
+
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    defer if (gpa.deinit() == .leak) log.err("memory leak", .{});
+
+    const allocator = gpa.allocator();
+
+    var app: App = .init(.{});
+    var renderer = zterm.Renderer.Buffered.init(allocator);
+    defer renderer.deinit();
+
+    var selection: App.Selection(enum {
+        one,
+        two,
+        three,
+    }) = .init(.{
+        .label = "Selection",
+    });
+    var quit_text: QuitText = .{};
+
+    var container = try App.Container.init(allocator, .{
+        .rectangle = .{ .fill = .grey },
+        .layout = .{ .padding = .all(5) },
+    }, quit_text.element());
+    defer container.deinit();
+    try container.append(try .init(allocator, .{}, selection.element()));
+
+    try app.start();
+    defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
+
+    // event loop
+    while (true) {
+        const event = app.nextEvent();
+        log.debug("received event: {s}", .{@tagName(event)});
+
+        // pre event handling
+        switch (event) {
+            .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
+            .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
+            else => {},
+        }
+
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
+            .err = .{
+                .err = err,
+                .msg = "Container Event handling failed",
+            },
+        });
+
+        // post event handling
+        switch (event) {
+            .quit => break,
+            else => {},
+        }
+
+        container.resize(try renderer.resize());
+        container.reposition(.{});
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
+        try renderer.flush();
+    }
+}
+
+pub const panic = App.panic_handler;
+const log = std.log.scoped(.default);
+
+const std = @import("std");
+const assert = std.debug.assert;
+const zterm = @import("zterm");
+const Error = zterm.Error;
+const App = zterm.App(struct {}, union(enum) {});

examples/errors.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -31,7 +31,7 @@ const InfoText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -57,7 +57,7 @@ const ErrorNotification = struct {
         return .{ .ptr = this, .vtable = &.{ .handle = handle, .content = content } };
     }
 
-    fn handle(ctx: *anyopaque, event: App.Event) !void {
+    fn handle(ctx: *anyopaque, _: *App.Model, event: App.Event) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         switch (event) {
             .key => |key| if (!key.isAscii()) return zterm.Error.TooSmall,
@@ -66,7 +66,7 @@ const ErrorNotification = struct {
         }
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         const this: *@This() = @ptrCast(@alignCast(ctx));
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -97,7 +97,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -130,7 +130,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -145,7 +145,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -156,4 +156,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/grid.zig

@@ -8,7 +8,7 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -35,7 +35,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -86,7 +86,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -101,7 +101,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -112,4 +112,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/horizontal.zig

@@ -8,7 +8,7 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -35,7 +35,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -78,7 +78,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -93,7 +93,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -104,4 +104,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/mixed.zig

@@ -8,7 +8,7 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -35,7 +35,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -94,7 +94,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -109,7 +109,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -120,4 +120,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/layouts/vertical.zig

@@ -8,7 +8,7 @@ const QuitText = struct {
         };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -35,7 +35,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -77,7 +77,7 @@ pub fn main() !void {
         }
 
         // NOTE returned errors should be propagated back to the application
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -92,7 +92,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -103,4 +103,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/styles/palette.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -32,7 +32,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -73,7 +73,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -88,7 +88,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -99,4 +99,4 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+const App = zterm.App(struct {}, union(enum) {});

examples/styles/text.zig

@@ -5,7 +5,7 @@ const QuitText = struct {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
 
@@ -28,10 +28,25 @@ const TextStyles = struct {
     const text = "Example";
 
     pub fn element(this: *@This()) App.Element {
-        return .{ .ptr = this, .vtable = &.{ .content = content } };
+        return .{
+            .ptr = this,
+            .vtable = &.{
+                .minSize = minSize,
+                .content = content,
+            },
+        };
     }
 
-    fn content(ctx: *anyopaque, cells: []zterm.Cell, size: zterm.Point) !void {
+    fn minSize(ctx: *anyopaque, size: zterm.Point) zterm.Point {
+        _ = ctx;
+        _ = size;
+        return .{
+            .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
+            .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
+        };
+    }
+
+    fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
         @setEvalBranchQuota(10000);
         _ = ctx;
         assert(cells.len == @as(usize, size.x) * @as(usize, size.y));
@@ -83,7 +98,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    var app: App = .init;
+    var app: App = .init(.{});
     var renderer = zterm.Renderer.Buffered.init(allocator);
     defer renderer.deinit();
 
@@ -102,12 +117,6 @@ pub fn main() !void {
 
     var box = try App.Container.init(allocator, .{
         .layout = .{ .direction = .vertical },
-        .size = .{
-            .dim = .{
-                .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
-                .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
-            },
-        },
     }, text_styles.element());
     defer box.deinit();
 
@@ -128,7 +137,7 @@ pub fn main() !void {
             else => {},
         }
 
-        container.handle(event) catch |err| app.postEvent(.{
+        container.handle(&app.model, event) catch |err| app.postEvent(.{
             .err = .{
                 .err = err,
                 .msg = "Container Event handling failed",
@@ -143,7 +152,7 @@ pub fn main() !void {
 
         container.resize(try renderer.resize());
         container.reposition(.{});
-        try renderer.render(@TypeOf(container), &container);
+        try renderer.render(@TypeOf(container), &container, App.Model, &app.model);
         try renderer.flush();
     }
 }
@@ -154,4 +163,5 @@ const log = std.log.scoped(.default);
 const std = @import("std");
 const assert = std.debug.assert;
 const zterm = @import("zterm");
-const App = zterm.App(union(enum) {});
+
+const App = zterm.App(struct {}, union(enum) {});

src/app.zig

@@ -12,18 +12,19 @@
 /// ```zig
 ///   const zterm = @import("zterm");
 ///   const App = zterm.App(
-///       union(enum) {},
+///       struct {}, // empty model
+///       union(enum) {}, // no additional user event's
 ///   );
 ///   // later on create an `App` instance and start the event loop
-///   var app: App = .init;
+///   var app: App = .init(.{}); // provide instance of the model that shall be used
 ///   try app.start();
-///   defer app.stop() catch unreachable;
+///   defer app.stop() catch unreachable; // does not clean-up the resources used in the model
 /// ```
-pub fn App(comptime E: type) type {
-    if (!isTaggedUnion(E)) {
-        @compileError("Provided user event `E` for `App(comptime E: type)` is not of type `union(enum)`.");
-    }
+pub fn App(comptime M: type, comptime E: type) type {
+    if (!isStruct(M)) @compileError("Provided model `M` for `App(comptime M: type, comptime E: type)` is not of type `struct`");
+    if (!isTaggedUnion(E)) @compileError("Provided user event `E` for `App(comptime M: type, comptime E: type)` is not of type `union(enum)`.");
     return struct {
+        model: Model,
         queue: Queue,
         thread: ?Thread = null,
         quit_event: Thread.ResetEvent,
@@ -33,17 +34,20 @@ pub fn App(comptime E: type) type {
         // global variable for the registered handler for WINCH
         var handler_ctx: *anyopaque = undefined;
         /// registered WINCH handler to report resize events
-        fn handleWinch(_: c_int) callconv(.C) void {
+        fn handleWinch(_: std.os.linux.SIG) callconv(.c) void {
             const this: *@This() = @ptrCast(@alignCast(handler_ctx));
             // NOTE this does not have to be done if in-band resize events are supported
             // -> the signal might not work correctly when hosting the application over ssh!
             this.postEvent(.resize);
         }
 
-        pub const init: @This() = .{
-            .queue = .{},
-            .quit_event = .{},
-        };
+        pub fn init(model: Model) @This() {
+            return .{
+                .model = model,
+                .queue = .{},
+                .quit_event = .unset,
+            };
+        }
 
         pub fn start(this: *@This()) !void {
             if (this.thread) |_| return;
@@ -69,8 +73,8 @@ pub fn App(comptime E: type) type {
             try terminal.enableRawMode(&termios);
             if (this.termios) |_| {} else this.termios = termios;
 
-            try terminal.saveScreen();
             try terminal.enterAltScreen();
+            try terminal.saveScreen();
             try terminal.hideCursor();
             try terminal.enableMouseSupport();
         }
@@ -78,8 +82,8 @@ pub fn App(comptime E: type) type {
         pub fn interrupt(this: *@This()) !void {
             this.quit_event.set();
             try terminal.disableMouseSupport();
-            try terminal.exitAltScreen();
             try terminal.restoreScreen();
+            try terminal.exitAltScreen();
             if (this.thread) |thread| {
                 thread.join();
                 this.thread = null;
@@ -88,12 +92,12 @@ pub fn App(comptime E: type) type {
 
         pub fn stop(this: *@This()) !void {
             try this.interrupt();
-            if (this.termios) |*termios| {
+            if (this.termios) |termios| {
                 try terminal.disableMouseSupport();
                 try terminal.showCursor();
-                try terminal.exitAltScreen();
-                try terminal.disableRawMode(termios);
                 try terminal.restoreScreen();
+                try terminal.disableRawMode(&termios);
+                try terminal.exitAltScreen();
             }
             this.termios = null;
         }
@@ -376,8 +380,8 @@ pub fn App(comptime E: type) type {
                             },
                             0x7f => .{ .cp = input.Backspace },
                             else => {
-                                var iter = code_point.Iterator{ .bytes = buf[0..read_bytes] };
-                                while (iter.next()) |cp| this.postEvent(.{ .key = .{ .cp = cp.code } });
+                                var iter: std.unicode.Utf8Iterator = .{ .bytes = buf[0..read_bytes], .i = 0 };
+                                while (iter.nextCodepoint()) |cp| this.postEvent(.{ .key = .{ .cp = cp } });
                                 continue;
                             },
                         };
@@ -391,9 +395,9 @@ pub fn App(comptime E: type) type {
 
         pub fn panic_handler(msg: []const u8, _: ?*std.builtin.StackTrace, ret_addr: ?usize) noreturn {
             terminal.disableMouseSupport() catch {};
-            terminal.exitAltScreen() catch {};
             terminal.showCursor() catch {};
-            var termios: posix.termios = .{
+            terminal.restoreScreen() catch {};
+            terminal.disableRawMode(&.{
                 .iflag = .{},
                 .lflag = .{},
                 .cflag = .{},
@@ -402,21 +406,23 @@ pub fn App(comptime E: type) type {
                 .line = 0,
                 .ispeed = undefined,
                 .ospeed = undefined,
-            };
-            terminal.disableRawMode(&termios) catch {};
-            terminal.restoreScreen() catch {};
+            }) catch {};
+            terminal.exitAltScreen() catch {};
             std.debug.defaultPanic(msg, ret_addr);
         }
 
         const element = @import("element.zig");
+        pub const Model = M;
         pub const Event = mergeTaggedUnions(event.SystemEvent, E);
-        pub const Container = @import("container.zig").Container(Event);
-        pub const Element = element.Element(Event);
-        pub const Alignment = element.Alignment(Event);
-        pub const Button = element.Button(Event, Queue);
-        pub const Input = element.Input(Event, Queue);
-        pub const Progress = element.Progress(Event, Queue);
-        pub const Scrollable = element.Scrollable(Event);
+        pub const Container = @import("container.zig").Container(Model, Event);
+        pub const Element = element.Element(Model, Event);
+        pub const Alignment = element.Alignment(Model, Event);
+        pub const Button = element.Button(Model, Event, Queue);
+        pub const Input = element.Input(Model, Event, Queue);
+        pub const Progress = element.Progress(Model, Event, Queue);
+        pub const RadioButton = element.RadioButton(Model, Event);
+        pub const Scrollable = element.Scrollable(Model, Event);
+        pub const Selection = element.Selection(Model, Event);
         pub const Queue = queue.Queue(Event, 256);
     };
 }
@@ -429,13 +435,13 @@ const fmt = std.fmt;
 const posix = std.posix;
 const Thread = std.Thread;
 const assert = std.debug.assert;
-const code_point = @import("code_point");
 const event = @import("event.zig");
 const input = @import("input.zig");
 const terminal = @import("terminal.zig");
 const queue = @import("queue.zig");
 const mergeTaggedUnions = event.mergeTaggedUnions;
 const isTaggedUnion = event.isTaggedUnion;
+const isStruct = event.isStruct;
 const Mouse = input.Mouse;
 const Key = input.Key;
 const Point = @import("point.zig").Point;

src/cell.zig

@@ -13,7 +13,7 @@ pub fn reset(this: *Cell) void {
     this.cp = ' ';
 }
 
-pub fn value(this: Cell, writer: anytype) !void {
+pub fn value(this: Cell, writer: *std.Io.Writer) !void {
     try this.style.value(writer, this.cp);
 }
 
@@ -29,17 +29,15 @@ test "ascii styled text" {
         .{ .cp = 's', .style = .{ .fg = .light_green, .bg = .black, .emphasis = &.{.underline} } },
     };
 
-    var string = std.ArrayList(u8).init(std.testing.allocator);
-    defer string.deinit();
-
-    const writer = string.writer();
+    var writer = std.Io.Writer.Allocating.init(std.testing.allocator);
+    defer writer.deinit();
     for (cells) |cell| {
-        try cell.value(writer);
+        try cell.value(&writer.writer);
     }
     try std.testing.expectEqualSlices(
         u8,
         "\x1b[38;5;10;48;5;8;59mY\x1b[0m\x1b[39;49;59;1;4mv\x1b[0m\x1b[39;49;59;3me\x1b[0m\x1b[38;5;2;48;5;16;59;4ms\x1b[0m",
-        string.items,
+        writer.writer.buffer[0..writer.writer.end],
     );
 }
 
@@ -51,16 +49,14 @@ test "utf-8 styled text" {
         .{ .cp = '┘', .style = .{ .fg = .light_green, .bg = .black, .emphasis = &.{.underline} } },
     };
 
-    var string = std.ArrayList(u8).init(std.testing.allocator);
-    defer string.deinit();
-
-    const writer = string.writer();
+    var writer = std.Io.Writer.Allocating.init(std.testing.allocator);
+    defer writer.deinit();
     for (cells) |cell| {
-        try cell.value(writer);
+        try cell.value(&writer.writer);
     }
     try std.testing.expectEqualSlices(
         u8,
         "\x1b[38;5;10;48;5;8;59m╭\x1b[0m\x1b[39;49;59m─\x1b[0m\x1b[39;49;59m┄\x1b[0m\x1b[38;5;2;48;5;16;59;4m┘\x1b[0m",
-        string.items,
+        writer.writer.buffer[0..writer.writer.end],
     );
 }

src/color.zig

@@ -20,22 +20,21 @@ pub const Color = enum(u8) {
 
     // TODO might be useful to use the std.ascii stuff!
 
-    pub inline fn write(this: Color, writer: anytype, comptime coloring: enum { fg, bg, ul }) !void {
+    pub inline fn write(this: Color, writer: *std.Io.Writer, comptime coloring: enum { fg, bg, ul }) !void {
         if (this == .default) {
             switch (coloring) {
-                .fg => try format(writer, "39", .{}),
-                .bg => try format(writer, "49", .{}),
-                .ul => try format(writer, "59", .{}),
+                .fg => try writer.printAscii("39", .{}),
+                .bg => try writer.printAscii("49", .{}),
+                .ul => try writer.printAscii("59", .{}),
             }
         } else {
             switch (coloring) {
-                .fg => try format(writer, "38;5;{d}", .{@intFromEnum(this)}),
-                .bg => try format(writer, "48;5;{d}", .{@intFromEnum(this)}),
-                .ul => try format(writer, "58;5;{d}", .{@intFromEnum(this)}),
+                .fg => try writer.print("38;5;{d}", .{@intFromEnum(this)}),
+                .bg => try writer.print("48;5;{d}", .{@intFromEnum(this)}),
+                .ul => try writer.print("58;5;{d}", .{@intFromEnum(this)}),
             }
         }
     }
 };
 
 const std = @import("std");
-const format = std.fmt.format;

src/container.zig

@@ -1,3 +1,6 @@
+// FIX known issues:
+// - hold fewer instances of the `Allocator`
+
 /// Border configuration struct
 pub const Border = packed struct {
     /// Color to use for the border
@@ -77,8 +80,9 @@ pub const Border = packed struct {
     test "all sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .all,
@@ -89,14 +93,15 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.all.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.all.zon"));
     }
 
     test "vertical sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .vertical,
@@ -107,14 +112,15 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.vertical.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.vertical.zon"));
     }
 
     test "horizontal sides" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .green,
                 .sides = .horizontal,
@@ -125,7 +131,7 @@ pub const Border = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/border.horizontal.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/border.horizontal.zon"));
     }
 };
 
@@ -157,8 +163,9 @@ pub const Rectangle = packed struct {
     test "fill color overwrite parent fill" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{ .fill = .green },
         }, .{});
         try container.append(try .init(std.testing.allocator, .{
@@ -170,14 +177,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_parent_fill_without_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_fill_without_padding.zon"));
     }
 
     test "fill color padding to show parent fill" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .padding = .all(2),
             },
@@ -192,14 +200,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_parent_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_padding.zon"));
     }
 
     test "fill color padding to show parent fill (negative padding)" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .padding = .{
                     .top = -18,
@@ -219,14 +228,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_parent_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_parent_padding.zon"));
     }
 
     test "fill color spacer with padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -247,14 +257,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_padding.zon"));
     }
 
     test "fill color with gap" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -278,14 +289,15 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_gap.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_gap.zon"));
     }
 
     test "fill color with separator" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .rectangle = .{
                 .fill = .black,
             },
@@ -310,7 +322,7 @@ pub const Rectangle = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/rectangle_with_separator.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/rectangle_with_separator.zon"));
     }
 };
 
@@ -400,8 +412,9 @@ pub const Layout = packed struct {
     test "separator without gaps" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .separator = .{
                     .enabled = true,
@@ -415,14 +428,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_no_gaps.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_no_gaps.zon"));
     }
 
     test "separator without gaps with padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .padding = .all(1),
                 .separator = .{
@@ -437,14 +451,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_no_gaps_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_no_gaps_with_padding.zon"));
     }
 
     test "separator(2x) without gaps" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .layout = .{
                 .direction = .vertical,
                 .separator = .{
@@ -461,14 +476,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps.zon"));
     }
 
     test "separator(2x) with border(all)" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -488,14 +504,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps_with_border.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps_with_border.zon"));
     }
 
     test "separator(2x) with border(all) and padding(all(1))" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -516,14 +533,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_no_gaps_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_no_gaps_with_padding.zon"));
     }
 
     test "separator(2x) with border(all) and gap" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -544,14 +562,15 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_with_gaps_with_border.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_with_gaps_with_border.zon"));
     }
 
     test "separator(2x) with border(all) and gap and padding" {
         const event = @import("event.zig");
         const testing = @import("testing.zig");
+        const Model = struct {};
 
-        var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+        var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
             .border = .{
                 .color = .red,
                 .sides = .all,
@@ -573,7 +592,7 @@ pub const Layout = packed struct {
         try testing.expectContainerScreen(.{
             .y = 20,
             .x = 30,
-        }, &container, @import("test/container/separator_2x_with_gaps_with_border_with_padding.zon"));
+        }, @TypeOf(container), &container, Model, @import("test/container/separator_2x_with_gaps_with_border_with_padding.zon"));
     }
 };
 
@@ -588,10 +607,10 @@ pub const Size = packed struct {
     } = .both,
 };
 
-pub fn Container(comptime Event: type) type {
+pub fn Container(Model: type, Event: type) type {
     if (!isTaggedUnion(Event)) @compileError("Provided user event `Event` for `Container(comptime Event: type)`");
 
-    const Element = @import("element.zig").Element(Event);
+    const Element = @import("element.zig").Element(Model, Event);
     return struct {
         allocator: Allocator,
         origin: Point,
@@ -622,17 +641,17 @@ pub fn Container(comptime Event: type) type {
                 .size = .{},
                 .properties = properties,
                 .element = element,
-                .elements = std.ArrayList(@This()).init(allocator),
+                .elements = try std.ArrayList(@This()).initCapacity(allocator, 2),
             };
         }
 
-        pub fn deinit(this: *const @This()) void {
+        pub fn deinit(this: *@This()) void {
             for (this.elements.items) |*element| element.deinit();
-            this.elements.deinit();
+            this.elements.deinit(this.allocator);
         }
 
         pub fn append(this: *@This(), element: @This()) !void {
-            try this.elements.append(element);
+            try this.elements.append(this.allocator, element);
         }
 
         pub fn reposition(this: *@This(), origin: Point) void {
@@ -886,7 +905,7 @@ pub fn Container(comptime Event: type) type {
             this.grow_resize(this.size);
         }
 
-        pub fn handle(this: *const @This(), event: Event) !void {
+        pub fn handle(this: *const @This(), model: *Model, event: Event) !void {
             switch (event) {
                 .mouse => |mouse| if (mouse.in(this.origin, this.size)) {
                     // the element receives the mouse event with relative position
@@ -894,17 +913,14 @@ pub fn Container(comptime Event: type) type {
                     var relative_mouse: input.Mouse = mouse;
                     relative_mouse.x -= this.origin.x;
                     relative_mouse.y -= this.origin.y;
-                    try this.element.handle(.{ .mouse = relative_mouse });
-                    for (this.elements.items) |*element| try element.handle(event);
-                },
-                else => {
-                    try this.element.handle(event);
-                    for (this.elements.items) |*element| try element.handle(event);
+                    try this.element.handle(model, .{ .mouse = relative_mouse });
                 },
+                else => try this.element.handle(model, event),
             }
+            for (this.elements.items) |*element| try element.handle(model, event);
         }
 
-        pub fn content(this: *const @This()) ![]Cell {
+        pub fn content(this: *const @This(), model: *const Model) ![]Cell {
             if (this.size.x == 0 or this.size.y == 0) return Error.TooSmall;
 
             const cells = try this.allocator.alloc(Cell, @as(usize, this.size.x) * @as(usize, this.size.y));
@@ -915,7 +931,7 @@ pub fn Container(comptime Event: type) type {
             this.properties.border.content(cells, this.size);
             this.properties.rectangle.content(cells, this.size);
 
-            try this.element.content(cells, this.size);
+            try this.element.content(model, cells, this.size);
 
             // DEBUG render corresponding corners (except top left) of this `Container` *red*
             if (comptime build_options.debug) {
@@ -959,8 +975,9 @@ test {
 test "Container Fixed and Grow Size Vertical" {
     const event = @import("event.zig");
     const testing = @import("testing.zig");
+    const Model = struct {};
 
-    var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+    var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
         .layout = .{ .direction = .vertical },
     }, .{});
     try container.append(try .init(std.testing.allocator, .{
@@ -978,14 +995,15 @@ test "Container Fixed and Grow Size Vertical" {
     try testing.expectContainerScreen(.{
         .y = 20,
         .x = 30,
-    }, &container, @import("test/container/fixed_grow_vertical.zon"));
+    }, @TypeOf(container), &container, Model, @import("test/container/fixed_grow_vertical.zon"));
 }
 
 test "Container Fixed and Grow Size Horizontal" {
     const event = @import("event.zig");
     const testing = @import("testing.zig");
+    const Model = struct {};
 
-    var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{}, .{});
+    var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{}, .{});
     try container.append(try .init(std.testing.allocator, .{
         .size = .{
             .dim = .{ .x = 5 },
@@ -1001,5 +1019,5 @@ test "Container Fixed and Grow Size Horizontal" {
     try testing.expectContainerScreen(.{
         .y = 20,
         .x = 30,
-    }, &container, @import("test/container/fixed_grow_horizontal.zon"));
+    }, @TypeOf(container), &container, Model, @import("test/container/fixed_grow_horizontal.zon"));
 }

src/event.zig

@@ -21,15 +21,19 @@ pub const SystemEvent = union(enum) {
     key: Key,
     /// Mouse input event
     mouse: Mouse,
-    /// Focus event for mouse interaction
-    /// TODO this should instead be a union with a `Size` to derive which container / element the focus meant for
+    /// Focus event indicating that the application has gained the focus of the user
     focus: bool,
 };
 
+/// Merge the two provided `union(enum)` `A` and `B` to a tagged union containing all fields of both tagged unions in `comptime`.
+/// Declarations are not supported for `comptime` created types, see https://github.com/ziglang/zig/issues/6709 for details.
 pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
-    if (!isTaggedUnion(A) or !isTaggedUnion(B)) {
-        @compileError("Both types for merging tagged unions need to be of type `union(enum)`.");
-    }
+    // TODO maybe it makes sense to have a nested tagged union type (i.e. system: union(enum) and event: union(enum))
+    // - allows re-definition of system / built-in events
+    // - clearly shows which events are system / built-in ones and which are user defined events
+    // - the memory footprint for the nesting is not really harmful
+    if (!isTaggedUnion(A) or !isTaggedUnion(B)) @compileError("Both types for merging tagged unions need to be of type `union(enum)`.");
+
     const a_fields = @typeInfo(A).@"union".fields;
     const a_fields_tag = @typeInfo(A).@"union".tag_type.?;
     const a_enum_fields = @typeInfo(a_fields_tag).@"enum".fields;
@@ -54,11 +58,27 @@ pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
         i += 1;
     }
 
-    const log2_i = @bitSizeOf(@TypeOf(i)) - @clz(i);
+    // NOTE declarations are not supported for `comptime` types: https://github.com/ziglang/zig/issues/6709
+    // -> will lead to a compilation error when constructing the tagged union
+    //    at the end of this function in case at least one of the provided tagged
+    //    unions to merge contains declarations (which in this case can only be the
+    //    user provided one)
+    const a_enum_decls = @typeInfo(A).@"union".decls;
+    const b_enum_decls = @typeInfo(B).@"union".decls;
+    var decls: [a_enum_decls.len + b_enum_decls.len]std.builtin.Type.Declaration = undefined;
+    var j: usize = 0;
+    for (a_enum_decls) |decl| {
+        decls[j] = decl;
+        j += 1;
+    }
+    for (b_enum_decls) |decl| {
+        decls[j] = decl;
+        j += 1;
+    }
 
     const EventType = @Type(.{ .int = .{
         .signedness = .unsigned,
-        .bits = log2_i,
+        .bits = @bitSizeOf(@TypeOf(i)) - @clz(i),
     } });
 
     const Event = @Type(.{ .@"enum" = .{
@@ -76,19 +96,25 @@ pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
     } });
 }
 
-// Determine at `comptime` whether the provided type `E` is an `union(enum)`.
-pub fn isTaggedUnion(comptime E: type) bool {
-    switch (@typeInfo(E)) {
-        .@"union" => |u| {
-            if (u.tag_type) |_| {} else {
-                return false;
-            }
+/// Determine whether the provided type `T` is a tagged union: `union(enum)`.
+pub fn isTaggedUnion(comptime T: type) bool {
+    switch (@typeInfo(T)) {
+        .@"union" => |u| if (u.tag_type) |_| {} else {
+            return false;
         },
         else => return false,
     }
     return true;
 }
 
+/// Determine whether the provided type `T` is a `struct`.
+pub fn isStruct(comptime T: type) bool {
+    return switch (@typeInfo(T)) {
+        .@"struct" => |_| true,
+        else => false,
+    };
+}
+
 const std = @import("std");
 const input = @import("input.zig");
 const terminal = @import("terminal.zig");

src/queue.zig

@@ -215,7 +215,7 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
     // still full and the push in the other thread is still blocked
     // waiting for space.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s);
+    std.Thread.sleep(std.time.ns_per_s);
     // Finally, let that other thread go.
     try testing.expectEqual(1, q.pop());
 
@@ -225,7 +225,7 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
         try Thread.yield();
     // But we want to ensure that there's a second push waiting, so
     // here's another sleep.
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Another spurious wake...
     q.not_full.signal();
@@ -233,7 +233,7 @@ fn sleepyPop(q: *Queue(u8, 2)) !void {
     // And another chance for the other thread to see that it's
     // spurious and go back to sleep.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Pop that thing and we're done.
     try testing.expectEqual(2, q.pop());
@@ -270,14 +270,14 @@ test "Fill, block, fill, block" {
 fn sleepyPush(q: *Queue(u8, 1)) !void {
     // Try to ensure the other thread has already started trying to pop.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Spurious wake
     q.not_full.signal();
     q.not_empty.signal();
 
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Stick something in the queue so it can be popped.
     q.push(1);
@@ -286,7 +286,7 @@ fn sleepyPush(q: *Queue(u8, 1)) !void {
         try Thread.yield();
     // Give the other thread time to block again.
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
 
     // Spurious wake
     q.not_full.signal();
@@ -317,7 +317,7 @@ test "2 readers" {
     const t1 = try Thread.spawn(cfg, readerThread, .{&queue});
     const t2 = try Thread.spawn(cfg, readerThread, .{&queue});
     try Thread.yield();
-    std.time.sleep(std.time.ns_per_s / 2);
+    std.Thread.sleep(std.time.ns_per_s / 2);
     queue.push(1);
     queue.push(1);
     t1.join();

src/render.zig

@@ -58,10 +58,10 @@ pub const Buffered = struct {
     }
 
     /// Render provided cells at size (anchor and dimension) into the *virtual screen*.
-    pub fn render(this: *@This(), comptime T: type, container: *T) !void {
+    pub fn render(this: *@This(), comptime Container: type, container: *Container, comptime Model: type, model: *const Model) !void {
         const size: Point = container.size;
         const origin: Point = container.origin;
-        const cells: []const Cell = try container.content();
+        const cells: []const Cell = try container.content(model);
 
         if (cells.len == 0) return;
 
@@ -80,7 +80,7 @@ pub const Buffered = struct {
         // free immediately
         container.allocator.free(cells);
 
-        for (container.elements.items) |*element| try this.render(T, element);
+        for (container.elements.items) |*element| try this.render(Container, element, Model, model);
     }
 
     /// Write *virtual screen* to alternate screen (should be called once and last during each render loop iteration in the main loop).
@@ -88,7 +88,7 @@ pub const Buffered = struct {
         try terminal.hideCursor();
         // TODO measure timings of rendered frames?
         var cursor_position: ?Point = null;
-        const writer = terminal.writer();
+        var writer = terminal.writer();
         const s = this.screen;
         const vs = this.virtual_screen;
         for (0..this.size.y) |row| {
@@ -110,7 +110,7 @@ pub const Buffered = struct {
 
                 // render differences found in virtual screen
                 try terminal.setCursorPosition(.{ .y = @truncate(row), .x = @truncate(col) });
-                try cvs.value(writer);
+                try cvs.value(&writer);
                 // update screen to be the virtual screen for the next frame
                 s[idx] = vs[idx];
             }

src/style.zig

@@ -42,27 +42,27 @@ pub fn eql(this: Style, other: Style) bool {
 
 // TODO might be useful to use the std.ascii stuff!
 
-pub fn value(this: Style, writer: anytype, cp: u21) !void {
+pub fn value(this: Style, writer: *std.Io.Writer, cp: u21) !void {
     var buffer: [4]u8 = undefined;
     const bytes = try unicode.utf8Encode(cp, &buffer);
     assert(bytes > 0);
     // build ansi sequence for 256 colors ...
     // foreground
-    try format(writer, "\x1b[", .{});
+    try writer.printAscii("\x1b[", .{});
     try this.fg.write(writer, .fg);
     // background
-    try format(writer, ";", .{});
+    try writer.printAsciiChar(';', .{});
     try this.bg.write(writer, .bg);
     // underline
     // FIX assert that if the underline property is set that the ul style and the attribute for underlining is available
-    try format(writer, ";", .{});
+    try writer.printAsciiChar(';', .{});
     try this.ul.write(writer, .ul);
     // append styles (aka attributes like bold, italic, strikethrough, etc.)
-    for (this.emphasis) |attribute| try format(writer, ";{d}", .{@intFromEnum(attribute)});
-    try format(writer, "m", .{});
+    for (this.emphasis) |attribute| try writer.print(";{d}", .{@intFromEnum(attribute)});
+    try writer.printAsciiChar('m', .{});
     // content
-    try format(writer, "{s}", .{buffer[0..bytes]});
-    try format(writer, "\x1b[0m", .{});
+    try writer.printAscii(buffer[0..bytes], .{});
+    try writer.printAscii("\x1b[0m", .{});
 }
 
 // TODO implement helper functions for terminal capabilities:
@@ -73,6 +73,5 @@ const std = @import("std");
 const unicode = std.unicode;
 const meta = std.meta;
 const assert = std.debug.assert;
-const format = std.fmt.format;
 const Color = @import("color.zig").Color;
 const Style = @This();

src/terminal.zig

@@ -62,19 +62,25 @@ pub fn write(buf: []const u8) !usize {
     return try posix.write(posix.STDIN_FILENO, buf);
 }
 
-fn contextWrite(context: @This(), data: []const u8) anyerror!usize {
-    _ = context;
-    return try posix.write(posix.STDOUT_FILENO, data);
+fn drainFn(w: *std.Io.Writer, data: []const []const u8, splat: usize) error{WriteFailed}!usize {
+    _ = w;
+    if (data.len == 0 or splat == 0) return 0;
+    var len: usize = 0;
+
+    for (data) |bytes| len += posix.write(posix.STDOUT_FILENO, bytes) catch return error.WriteFailed;
+
+    return len;
 }
 
-const Writer = std.io.Writer(
-    @This(),
-    anyerror,
-    contextWrite,
-);
-
-pub fn writer() Writer {
-    return .{ .context = .{} };
+// TODO I now need to add that much, for just the one function above?
+pub fn writer() std.Io.Writer {
+    return .{
+        .vtable = &.{
+            .drain = drainFn,
+            .flush = std.Io.Writer.noopFlush,
+        },
+        .buffer = &.{},
+    };
 }
 
 pub fn setCursorPosition(pos: Point) !void {
@@ -191,7 +197,7 @@ pub fn enableRawMode(bak: *posix.termios) !void {
 }
 
 /// Reverts `enableRawMode` to restore initial functionality.
-pub fn disableRawMode(bak: *posix.termios) !void {
+pub fn disableRawMode(bak: *const posix.termios) !void {
     try posix.tcsetattr(
         posix.STDIN_FILENO,
         .FLUSH,
@@ -232,7 +238,7 @@ const log = std.log.scoped(.terminal);
 const std = @import("std");
 const mem = std.mem;
 const posix = std.posix;
-const code_point = @import("code_point");
+const assert = std.debug.assert;
 const ctlseqs = @import("ctlseqs.zig");
 const input = @import("input.zig");
 const Key = input.Key;

src/testing.zig

@@ -34,10 +34,10 @@ pub const Renderer = struct {
         @memset(this.screen, .{});
     }
 
-    pub fn render(this: *@This(), comptime T: type, container: *const T) !void {
+    pub fn render(this: *@This(), comptime T: type, container: *const T, comptime Model: type, model: *const Model) !void {
         const size: Point = container.size;
         const origin: Point = container.origin;
-        const cells: []const Cell = try container.content();
+        const cells: []const Cell = try container.content(model);
 
         if (cells.len == 0) return;
 
@@ -58,7 +58,7 @@ pub const Renderer = struct {
         // free immediately
         container.allocator.free(cells);
 
-        for (container.elements.items) |*element| try this.render(T, element);
+        for (container.elements.items) |*element| try this.render(T, element, Model, model);
     }
 
     pub fn save(this: @This(), writer: anytype) !void {
@@ -74,6 +74,8 @@ pub const Renderer = struct {
 /// Create a .zon file containing the expected `Cell` slice using the `zterm.testing.Renderer.save` method:
 ///
 /// ```zig
+/// const Model = struct {};
+/// var model: Model = .{};
 /// const file = try std.fs.cwd().createFile("test/container/border/all.zon", .{ .truncate = true });
 /// defer file.close();
 ///
@@ -81,8 +83,8 @@ pub const Renderer = struct {
 /// var renderer: testing.Renderer = .init(allocator, size);
 /// defer renderer.deinit();
 ///
-/// try container.handle(.{ .size = size });
-/// try renderer.render(Container(event.SystemEvent), &container);
+/// try container.handle(&model, .{ .size = size });
+/// try renderer.render(@TypeOf(container), &container, Model, &.{});
 /// try renderer.save(file.writer());
 /// ```
 ///
@@ -91,7 +93,8 @@ pub const Renderer = struct {
 /// Then later load that .zon file at compile time and run your test against this `Cell` slice.
 ///
 /// ```zig
-/// var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
+/// const Model = struct {};
+/// var container: Container(Model, event.SystemEvent) = try .init(std.testing.allocator, .{
 ///     .border = .{
 ///         .color = .green,
 ///         .sides = .all,
@@ -102,20 +105,55 @@ pub const Renderer = struct {
 /// try testing.expectContainerScreen(.{
 ///     .rows = 20,
 ///     .cols = 30,
-/// }, &container, @import("test/container/border.all.zon"));
+/// }, @TypeOf(container), &container, Model, @import("test/container/border.all.zon"));
 /// ```
-pub fn expectContainerScreen(size: Point, container: *Container(event.SystemEvent), expected: []const Cell) !void {
+pub fn expectContainerScreen(size: Point, comptime T: type, container: *T, comptime Model: type, expected: []const Cell) !void {
     const allocator = testing.allocator;
     var renderer: Renderer = .init(allocator, size);
     defer renderer.deinit();
 
     container.resize(size);
     container.reposition(.{});
-    try renderer.render(Container(event.SystemEvent), container);
+    try renderer.render(T, container, Model, &.{});
 
     try expectEqualCells(.{}, renderer.size, expected, renderer.screen);
 }
 
+/// Taken from: https://codeberg.org/atman/zg/src/branch/master/src/DisplayWidth.zig
+/// Owned by https://codeberg.org/atman licensed under MIT all credits for this function go to him
+fn center(allocator: Allocator, str: []const u8, total_width: usize, pad: []const u8) ![]u8 {
+    if (str.len > total_width) return error.StrTooLong;
+    if (str.len == total_width) return try allocator.dupe(u8, str);
+
+    if (pad.len > total_width or str.len + pad.len > total_width) return error.PadTooLong;
+
+    const margin_width = @divFloor((total_width - str.len), 2);
+    if (pad.len > margin_width) return error.PadTooLong;
+
+    const extra_pad: usize = if (total_width % 2 != str.len % 2) 1 else 0;
+    const pads = @divFloor(margin_width, pad.len) * 2 + extra_pad;
+
+    var result = try allocator.alloc(u8, pads * pad.len + str.len);
+    var bytes_index: usize = 0;
+    var pads_index: usize = 0;
+
+    while (pads_index < pads / 2) : (pads_index += 1) {
+        @memcpy(result[bytes_index..][0..pad.len], pad);
+        bytes_index += pad.len;
+    }
+
+    @memcpy(result[bytes_index..][0..str.len], str);
+    bytes_index += str.len;
+
+    pads_index = 0;
+    while (pads_index < pads / 2 + extra_pad) : (pads_index += 1) {
+        @memcpy(result[bytes_index..][0..pad.len], pad);
+        bytes_index += pad.len;
+    }
+
+    return result;
+}
+
 /// This function is intended to be used only in tests. Test if the two
 /// provided cell arrays are identical. Usually the `Cell` slices are
 /// the contents of a given screen from the `zterm.testing.Renderer`. See
@@ -127,28 +165,21 @@ pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actu
     try testing.expectEqual(expected.len, @as(usize, size.y) * @as(usize, size.x));
 
     var expected_cps = try std.ArrayList(Cell).initCapacity(allocator, size.x);
-    defer expected_cps.deinit();
+    defer expected_cps.deinit(allocator);
 
     var actual_cps = try std.ArrayList(Cell).initCapacity(allocator, size.x);
-    defer actual_cps.deinit();
+    defer actual_cps.deinit(allocator);
 
-    var output = try std.ArrayList(u8).initCapacity(allocator, expected_cps.capacity * actual_cps.capacity + 5 * size.y);
-    defer output.deinit();
+    var allocating_writer = std.Io.Writer.Allocating.init(allocator);
+    defer allocating_writer.deinit();
 
-    var buffer = std.io.bufferedWriter(output.writer());
-    defer buffer.flush() catch {};
-
-    const writer = buffer.writer();
+    var writer = &allocating_writer.writer;
     var differ = false;
 
-    const dwd = try DisplayWidth.DisplayWidthData.init(allocator);
-    defer dwd.deinit();
-    const dw: DisplayWidth = .{ .data = &dwd };
-
-    const expected_centered = try dw.center(allocator, "Expected Screen", size.x, " ");
+    const expected_centered = try center(allocator, "Expected Screen", size.x, " ");
     defer allocator.free(expected_centered);
 
-    const actual_centered = try dw.center(allocator, "Actual Screen", size.x, " ");
+    const actual_centered = try center(allocator, "Actual Screen", size.x, " ");
     defer allocator.free(actual_centered);
 
     try writer.print("Screens are not equivalent.\n{s} ┆ {s}\n", .{ expected_centered, actual_centered });
@@ -164,8 +195,8 @@ pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actu
 
             if (!expected_cell.eql(actual_cell)) differ = true;
 
-            try expected_cps.append(expected_cell);
-            try actual_cps.append(actual_cell);
+            try expected_cps.append(allocator, expected_cell);
+            try actual_cps.append(allocator, actual_cell);
         }
 
         // write screens both formatted to buffer
@@ -178,13 +209,14 @@ pub fn expectEqualCells(origin: Point, size: Point, expected: []const Cell, actu
     if (!differ) return;
 
     // test failed
-    try buffer.flush();
-
     debug.lockStdErr();
     defer debug.unlockStdErr();
 
-    const std_writer = std.io.getStdErr().writer();
-    try std_writer.writeAll(output.items);
+    var stdout_buffer: [1024]u8 = undefined;
+    var stdout = std.fs.File.stdout().writer(&stdout_buffer);
+    const stdout_writer = &stdout.interface;
+    try stdout_writer.writeAll(writer.buffer[0..writer.end]);
+    try stdout_writer.flush();
     return error.TestExpectEqualCells;
 }
 
@@ -195,5 +227,4 @@ const Allocator = std.mem.Allocator;
 const event = @import("event.zig");
 const Container = @import("container.zig").Container;
 const Cell = @import("cell.zig");
-const DisplayWidth = @import("DisplayWidth");
 const Point = @import("point.zig").Point;