extract-variant 1.0.0

Destructure expressions into, and return assignments from, a single pattern.
Documentation 
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use variant::try_variant;

struct Foo {
    a: Bar,
    b: Option<i8>,
}

enum Bar {
    A(u8),
    B(bool),
}

fn main() {
    let val = Foo { a: Bar::B(false), b: Some(-5) };
    let (i, j) = try_variant!(val, Foo { a: Bar::B(i), b: Some(j) }).expect("(i, j)");
    assert_eq!(i, false);
    assert_eq!(j, -5);

    let res = try_variant!(val, Foo { a: Bar::A(i), b: Some(j) });
    assert!(res.is_err());

    let _: () = try_variant!(val, Foo { a: Bar::B(_), .. }).expect("unit");

    // multiple extracted idents are lexicographically ordered in the resultant
    // tuple, regardless of where these assignments appear in the pattern.
    let val = Foo { a: Bar::B(true), b: Some(10) };
    let (a, b) = try_variant!(val, Foo { a: Bar::B(b), b: Some(a) }).expect("(a, b)");
    assert_eq!((a, b), (10, true));
}