macro_rules! never {
    (true $($tt:tt)*) => { ... };
    (false $($tt:tt)*) => { ... };
    () => { ... };
    ($fmt:literal $(, $($arg:tt)*)?) => { ... };
    ($cond:expr) => { ... };
    ($cond:expr, $fmt:literal $($arg:tt)*) => { ... };
}
Expand description

Asserts that the condition is never true and returns its actual value.

If the condition is false does nothing and and evaluates to false.

If the condition is true:

  • panics if force feature or debug_assertions are enabled,
  • logs an error if log feature is enabled,
  • evaluates to true.

Accepts format! style arguments.

Empty condition is equivalent to false:

never!("oups") ~= unreachable!("oups")