Macro std::unreachable

macro unreachable() { ... }

source

Treats the location as unreachable during program flow.

In debug mode, this macro will panic if ever reached. In release mode, it will cause undefined behavior. This is a way to satisfy type-checker, especially useful in switch expressions.

Example

let number: i32 = 42;
switch number % 3 {
    0 => "odd",
    1 => "even",
    2 => "what even?",
    _ => unreachable!()
};
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