Macro static_assertions::const_assert

macro_rules! const_assert {
    ($($xs:expr),+ $(,)*) => { ... };
    ($label:ident; $($xs:tt)+) => { ... };
}

Asserts at compile-time that the constant expression evaluates to true.

Example

const_assert!(2 + 2 == 4);

const FIVE: usize = 5;
const_assert!(FIVE - FIVE == 0);

// Produces a compilation failure:
// const_assert!(1 >= 2);