# Macro core::assert_matches::debug_assert_matches
[−][src]

    pub macro debug_assert_matches($($arg : tt) *) {
        ...
    }

🔬 This is a nightly-only experimental API. (`assert_matches` #82775)
Expand description

Asserts that an expression matches any of the given patterns.

Like in a `match` expression, the pattern can be optionally followed by `if` and a guard expression that has access to names bound by the pattern.

On panic, this macro will print the value of the expression with its debug representation.

Unlike `assert_matches!`, `debug_assert_matches!` statements are only enabled in non optimized builds by default. An optimized build will not execute `debug_assert_matches!` statements unless `-C debug-assertions` is passed to the compiler. This makes `debug_assert_matches!` useful for checks that are too expensive to be present in a release build but may be helpful during development. The result of expanding `debug_assert_matches!` is always type checked.

## Examples

    #![feature(assert_matches)]

    use std::assert_matches::debug_assert_matches;

    let a = 1u32.checked_add(2);
    let b = 1u32.checked_sub(2);
    debug_assert_matches!(a, Some(_));
    debug_assert_matches!(b, None);

    let c = Ok("abc".to_string());
    debug_assert_matches!(c, Ok(x) | Err(x) if x.len() < 100);

Run