std::macros::assert

macro_rules! assert(
    ($cond:expr) => (
        if !$cond {
            fail!("assertion failed: {:s}", stringify!($cond))
        }
    );
    ($cond:expr, $msg:expr) => (
        if !$cond {
            fail!($msg)
        }
    );
    ($cond:expr, $($arg:expr),+) => (
        if !$cond {
            fail!($($arg),+)
        }
    );
)

Ensure that a boolean expression is true at runtime.

This will invoke the fail! macro if the provided expression cannot be evaluated to true at runtime.

Example

// the failure message for these assertions is the stringified value of the
// expression given.
assert!(true);
assert!(some_computation());

// assert with a custom message
assert!(x, "x wasn't true!");
assert!(a + b == 30, "a = {}, b = {}", a, b);