comptime in Zig

The same language runs at compile time: a Fibonacci number baked into the binary.

const std = @import("std");

// Anything computable from constants can run during compilation.
fn fib(n: u32) u32 {
    if (n < 2) return n;
    return fib(n - 1) + fib(n - 2);
}

pub fn main() void {
    const at_build = comptime fib(12);
    std.debug.print("fib(12) baked into the binary: {d}\n", .{at_build});

    comptime var total = 0;
    inline for (.{ 3, 5, 7 }) |x| total += x;
    std.debug.print("summed during compilation: {d}\n", .{total});
}

How it works

1. comptime fib(12) runs the recursion during compilation; the binary holds 144.
2. comptime var mutates during compilation only.
3. inline for unrolls over the tuple, folding the sum before the program exists.

Keywords and builtins used here

• comptime
• const
• fn
• for
• if
• inline
• pub
• return
• u32
• var
• void

The run, in numbers

Lines

16

Characters to type

429

Tokens

122

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 113 seconds.

Type this snippet

Step 1 of 3 in comptime, step 16 of 27 in Language basics.

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