static_assertions 0.2.5

Compile-time assertions to ensure that invariants are met.

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Rust compile-time assertions to ensure that invariants are met.



This crate is available on and can be used by adding the following to your project's Cargo.toml:

static_assertions = "0.2.5"

and this to your crate root:

extern crate static_assertions;


Assert Equal Size

Use assert_eq_size! to ensure two types are the same size:

// Requires a label if in module scope
assert_eq_size!(byte; u8, u8);

fn func() {
    // If label-less, must be in a function to work
    assert_eq_size!([u8; 4], u32);

    // Supports unlimited arguments
    assert_eq_size!([u8; 8], u64, (u32, u32), (u32, u16, u16), ...);

    // Fails to compile
    assert_eq_size!(u16, u64);

Use assert_eq_size_val! to ensure two values are the same size:

let x: u32 = 42;
let y: u32 = 10;
assert_eq_size_val!(x, y, [0u8; 4]);

// Fails to compile
assert_eq_size_val!(x, 0u8);

Note: Both macros support multiple arguments and are not restricted by the recursion limit.

Assert Constant Expression

A constant expression can be ensured to evaluate to true at compile-time.

The const_assert and const_assert_eq macros have the same scope and label limitations as assert_eq_size.

// Supports constants
const FIVE: usize = 5;

fn func() {
    const_assert!(1 + 1 == 2);

    // Supports unlimited comma-separated conditions
    const_assert!(4 > 3, 3 + 2 == FIVE);

    // Fails to compile
    const_assert!(2 != 2);


See issue #1 to read up on current limitations of this crate and how to currently overcome them.


This project is released under either:

at your choosing.