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Zig Academy · Lesson

Building Types with @Type

Construct new types programmatically.

Building Types with @Type is a free Zig Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Zig Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

The Reverse of @typeInfo

If @typeInfo turns a type into data, @Type turns data back into a real type. Together they let you reshape types at compile time. 🛠️

Feed It a Type.Info Value

@Type takes a std.builtin.Type value and produces the concrete type it describes. You hand it a description, it gives you a type.

const T = @Type(.{ .Int = .{ .signedness = .unsigned, .bits = 8 } });

Build an Integer Type

The example above constructs u8 from scratch. Change bits to 16 and you get u16, all decided while the program compiles.

const U16 = @Type(.{ .Int = .{ .signedness = .unsigned, .bits = 16 } });

Round-Trip a Type

Passing a type through @typeInfo then @Type returns the very same type. This proves the two builtins are exact inverses.

const Same = @Type(@typeInfo(u32));

Describe a Struct as Data

To build a struct you fill in a StructField array. Each field needs a name, a type, alignment, and a default pointer.

const f = std.builtin.Type.StructField;

Assemble the Struct Payload

Wrap your fields in a .Struct payload with a layout and an is_tuple flag, then hand the whole thing to @Type.

const info = .{ .Struct = .{
    .layout = .auto,
    .fields = my_fields,
    .decls = &.{},
    .is_tuple = false,
} };

Generate a Fresh Struct Type

Call @Type on that payload and you get a brand-new struct type, built by your own logic rather than written by hand.

const Generated = @Type(info);

Defaults Need a Comptime Pointer

A field's default_value is an optional const pointer to the value, or null when there is no default. The pointer must be comptime-known.

const dv: ?*const anyopaque = &@as(u8, 0);

Build Enums and More

The same trick works beyond structs: the .Enum payload lets @Type synthesize enum types from a computed list of members.

Why Construct Types at All

Generated types power serializers and ORMs: derive a packed config or row type automatically instead of editing it by hand. ✨

Pair It with Reflection

The strongest pattern reads a type with @typeInfo, transforms the data, then rebuilds a new type with @Type, like adding a field.

Quick Check

You have a std.builtin.Type value describing a struct. What turns it into a usable type?

Recap

@Type builds real types from Type.Info data, the inverse of @typeInfo. Pair them to read, transform, and regenerate types. 🎯

Frequently asked questions

Is the “Building Types with @Type” lesson free?

Yes — the full text of “Building Types with @Type” is free to read here on the web, and the Zig Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Zig Academy course, upgrade to CoddyKit PRO.

What will I learn in “Building Types with @Type”?

Construct new types programmatically. You practise Zig Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Zig Academy?

No prior experience is required. Zig Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Building Types with @Type” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Zig Academy lesson?

Yes. Every Zig Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Reflecting Fields with @typeInfo
  2. Building Types with @Type
  3. Comptime Validation and @compileError
  4. Generating Code with comptime
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