Macro core_extensions::matches

macro_rules! matches {
    ( $(|)* $pat:pat $(| $prev_pat:pat)*  =$expr:expr) => { ... };
}

Macro that evaluates to true if the expression matches any of the patterns (this macro can have multiple patterns).

Example

use std::num::ParseIntError;

#[derive(Debug,Copy,Clone)]
pub struct Even(u64);

impl Even{
    fn value(self)->u64{ self.0 }

    fn parse(n:&str)->Result<Option<Even>,ParseIntError>{
        match n.parse::<u64>() {
            Ok(v)if v%2==0 =>Ok(Some(Even(v))),
            Ok(v)          =>Ok(None),
            Err(e)=>Err(e),
        }
    }
}

let mut even_nums=0;
for i in 0..11 {
    let parsed=Even::parse(&i.to_string());
    if let Ok(Some(Even(j)))=parsed{
        assert_eq!(i,j);
        even_nums+=1;
    }
    assert!(matches!(
        |Ok(Some(Even(0)))
        |Ok(Some(Even(2)))
        |Ok(Some(Even(4)))
        |Ok(Some(Even(6)))
        |Ok(Some(Even(8)))
        |Ok(Some(Even(10)))
        |Ok(None)
        =parsed
    ));
    assert!( ! matches!( Err(_)=parsed ));
}
assert_eq!(even_nums,6);

assert!(   matches!( Ok(Some(Even(0))) =Even::parse("0") ));
assert!( ! matches!( Ok(None)          =Even::parse("0") ));

assert!(   matches!( Ok(None   )       =Even::parse("1") ));
assert!( ! matches!( Ok(Some(_))       =Even::parse("1") ));

assert!(   matches!( Ok(Some(Even(2))) =Even::parse("2") ));
assert!( ! matches!( Ok(None         ) =Even::parse("2") ));

assert!(   matches!( Ok(None   )       =Even::parse("3") ));
assert!( ! matches!( Ok(Some(_))       =Even::parse("3") ));

assert!(   matches!( Err(_)            =Even::parse("what") ));
assert!( ! matches!( Ok (_)            =Even::parse("what") ));

assert!(   matches!( |Err(_)            =Even::parse("1a") ));
assert!( ! matches!( |Ok (_)            =Even::parse("1a") ));

// you can prefix the first pattern with any ammount of space separated '|'.
// "||" is parsed as a short-circuiting logical or.
assert!(   matches!( | | Err(_)            =Even::parse("-1") ));
assert!( ! matches!( | | Ok (_)            =Even::parse("-1") ));