Generating Code with comptime
Emit repetitive logic automatically.
Generating Code with comptime is a free Zig Academy lesson on CoddyKit — lesson 4 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.
Let the Compiler Write Repetition
Instead of copying near-identical code, you describe the pattern once and let comptime emit each variation for you. ⚙️
inline for Unrolls the Loop
An inline for over a comptime list expands into separate statements, one per item, all baked into the final program.
inline for (.{ 1, 2, 3 }) |n| {
std.debug.print("{}\n", .{n});
}Loop Over a Type's Fields
Combine reflection with unrolling: walk every field of a struct and generate matching code for each one automatically.
inline for (@typeInfo(T).Struct.fields) |field| {
std.debug.print("{s}\n", .{field.name});
}Access Fields by Name
Use @field to read a field whose name is a comptime string. This is how generated code touches each field generically.
const value = @field(my_struct, field.name);Build a Generic Printer
Together these tools let you write one function that prints any struct, expanding to handle each field at compile time.
inline for (@typeInfo(@TypeOf(s)).Struct.fields) |f| {
std.debug.print("{s}={any}\n", .{ f.name, @field(s, f.name) });
}Generate Declarations in a Type
Inside a type-returning function you can run loops and conditionals, then return struct to bake the computed shape into a type.
fn Vec(comptime n: usize) type {
return struct { data: [n]f32 };
}Switch Generates Per-Variant Code
A switch on a comptime tag compiles to just the chosen branch, so you can specialize behavior for each enum or union case.
comptime Blocks Run Early
Wrap setup in a comptime block to compute lookup tables or constants once, during the build, with no run-time work.
const table = comptime blk: {
var t: [4]u8 = undefined;
break :blk t;
};This Replaces Macros
Where C reaches for the preprocessor, Zig uses ordinary code at compile time. The same language writes both your program and its generator.
Keep Generated Code Honest
Pair generation with @compileError guards so unsupported shapes fail clearly instead of producing surprising output.
Powerful but Readable
Because it is just Zig, generated logic stays debuggable and type-checked. You get macro power without a separate language. ✨
Quick Check
You want to emit one statement per struct field at compile time. Which construct unrolls the field list?
Recap
With inline for, @field, and type-returning functions, comptime generates repetitive code safely, replacing C macros. 🎯
Frequently asked questions
Is the “Generating Code with comptime” lesson free?
Yes — the full text of “Generating Code with comptime” 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 “Generating Code with comptime”?
Emit repetitive logic automatically. 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 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Generating Code with comptime” 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
- Reflecting Fields with @typeInfo
- Building Types with @Type
- Comptime Validation and @compileError
- Generating Code with comptime