Version: 1.1.0

Compile-time evaluation

comptime runs code during compilation and leaves a constant behind. Loops, conditions, and pure calculations are all available.

Essentials

• comptime if keeps one branch and deletes the other.
• comptime for unrolls a loop whose trip count is a parameter.
• A comptime value can become a runtime value by using it in ordinary code.
• Side effects that need a running process do not belong in comptime.

Example

fn pow2[n: Int]() -> Int:
    var acc = 1
    comptime:
        for _ in range(n):
            acc *= 2
    return acc

Keep in mind

Unrolling helps tiny kernels. It hurts when the generated code gets larger than the instruction cache.