Macro matux::expect

macro_rules! expect {
    ($src:expr, $pat:pat => $proj:expr, $msg:literal $(, $args:expr)*) => { ... };
}

Asserts that an expression follows a pattern; otherwise fail with an error message.

Example

#[derive(Debug)]
enum A {
    B(&'static str),
    C(u32),
}

let c = A::C(3);
let inner = matux::expect!(c, A::C(x) => x, "c is not A::C but {:?}", c);
assert_eq!(inner, 3u32);

#[derive(Debug)]
enum A {
    B(&'static str),
    C(u32),
}

let c = A::C(3);
matux::expect!(c, A::B(x) => x, "c is not A::B but {:?}", c); // Panic: "c is not A::B but C(3)"