Const Generics for Zero-Cost Abstraction

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Const Generics for Zero-Cost Abstraction

Const generics allow compile-time constants as generic parameters. Unlike type parameters that accept types, const parameters accept compile-time constant values like integer literals. This enables creating truly generic containers whose size is determined at compile time, with zero runtime overhead.

snippet.rs
rust
struct Matrix<T, const N: usize, const M: usize> {
    data: [[T; M]; N],
}
 
impl<T, const N: usize, const M: usize> Matrix<T, N, M>
where
    T: Default + Copy,
{
    fn new() -> Self {
        Self { data: [[T::default(); M]; N] }
    }
}
 
fn main() {
    let m: Matrix<i32, 2, 3> = Matrix::new();
    println!("Matrix size: {}x{}", 2, 3);
}

Breakdown

const N: usize, const M: usize

Declares const generic parameters N and M of type usize for dimensions

data: [[T; M]; N]

Creates a 2D array of type T with dimensions N x M, all known at compile time

where T: Default + Copy,

Requires T to be Default-constructible and Copy for stack-based storage

[[T::default(); M]; N]

Creates array by repeating default value M times for N rows

let m: Matrix<i32, 2, 3> = Matrix::new();

Creates a 2x3 matrix with specific compile-time dimensions

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Const Generics for Zero-Cost Abstraction

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