Add a macro that evaluates to Option<_>

[yvt]

This issue proposes to add a variation of try_match! that evaluates to Option instead of Result.

Prior Arts

• bind_match::bind_match! from bind_match
• extract::extract! from extract_macro
• variant::get_variant! from extract-variant
• matches2::option_match! from matches2
• Result::ok matches self against Ok(x) and returns Some(x).

Issues

• What should it be called? A few candidates:
  • try_match_ok!($expr, $pat) (try_match! + Result::ok)
  • match_ok!($expr, $pat) (match + Result::ok)
  • get_match!($expr, $pat)

Examples

Iterator::filter_map

let array = [Var1(42), Var2, Var1(10)];
let filtered: Vec<_> = array
    .iter()
    .filter_map(|x| try_match_ok!(x, &Var1(_0) if _0 > 20))
    .collect();
assert_eq!(filtered, [42]);

Combined with #3:

let array = [Var1(42), Var2, Var1(10)];
let filtered: Vec<_> = array
    .iter()
    .filter_map(try_match_ok!(, &Var1(_0) if _0 > 20))
    .collect();
assert_eq!(filtered, [42]);

Extracting Variants

impl<T> Enum<T> {
    fn var1(&self) -> Option<&T> {
        try_match_ok!(self, Var1(_0))
    }

    fn is_var2(&self) -> bool {
        matches!(self, Var2)
    }
}

[yvt]

Unstably added in commit f3137df

[yvt]

Change of plan: Insta-stabilized the feature in commit 293993e.