Macro assert_matches

macro_rules! assert_matches {
    ( $e:expr , $($pat:pat)|+ ) => { ... };
    ( $e:expr , $($pat:pat)|+ if $cond:expr ) => { ... };
    ( $e:expr , $($pat:pat)|+ => $arm:expr ) => { ... };
    ( $e:expr , $($pat:pat)|+ if $cond:expr => $arm:expr ) => { ... };
    ( $e:expr , $($pat:pat)|+ , $($arg:tt)* ) => { ... };
    ( $e:expr , $($pat:pat)|+ if $cond:expr , $($arg:tt)* ) => { ... };
    ( $e:expr , $($pat:pat)|+ => $arm:expr , $($arg:tt)* ) => { ... };
    ( $e:expr , $($pat:pat)|+ if $cond:expr => $arm:expr , $($arg:tt)* ) => { ... };
}

Asserts that an expression matches a given pattern.

A guard expression may be supplied to add further restrictions to the expected value of the expression.

A match arm may be supplied to perform additional assertions or to yield a value from the macro invocation.

Examples

#[macro_use] extern crate assert_matches;

#[derive(Debug)]
enum Foo {
    A(i32),
    B(&'static str),
}

let a = Foo::A(1);

// Assert that `a` matches the pattern `Foo::A(_)`.
assert_matches!(a, Foo::A(_));

// Assert that `a` matches the pattern and
// that the contained value meets the condition `i > 0`.
assert_matches!(a, Foo::A(i) if i > 0);

let b = Foo::B("foobar");
 
// Assert that `b` matches the pattern `Foo::B(_)`.
assert_matches!(b, Foo::B(s) => {
    // Perform additional assertions on the variable binding `s`.
    assert!(s.starts_with("foo"));
    assert!(s.ends_with("bar"));
});

// Assert that `b` matches the pattern and yield the string `s`.
let s = assert_matches!(b, Foo::B(s) => s);

// Perform an assertion on the value `s`.
assert_eq!(s, "foobar");