rust 11 lines · 1 tab

const and const fn for compile-time evaluation

Marcus Chen Jan 2026

1 tab

const MAX_SIZE: usize = 1024;

const fn square(n: u32) -> u32 {
    n * n
}

const RESULT: u32 = square(5);

fn main() {
    println!("Square of 5: {}", RESULT);
}

1 file · rust Explain with highlit

const defines compile-time constants, and const fn are functions that can run at compile time. I use const for magic numbers, lookup tables, and configuration that never changes. const fn is powerful for building complex constants (like hash maps or arrays) without runtime cost. The restrictions are tight: no heap allocation, no panic, limited operations. As Rust evolves, more features become const-compatible. I use const fn for validators, hash functions, and array initialization. The benefit is zero runtime cost: the computation happens during compilation. For performance-critical code, moving work to compile time can eliminate entire code paths at runtime.

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