Macro ident 

macro_rules! ident {
    (
        $(#[$meta:meta])*
        pub <$ty_a:ty, $ty_b:ty>: [ $( $a:expr => $b:expr ),+ ]
    ) => { ... };
    (
        $(#[$meta:meta])*
        <$ty_a:ty, $ty_b:ty>: [ $( $a:expr => $b:expr ),+ ]
    ) => { ... };
}

Create identity functions for Eq types

generates two functions

fn ident_to(a: &A)   -> Option<&'static B> { /* ... */ }
fn ident_from(b: &B) -> Option<&'static A> { /* ... */ }

Examples

struct Scopes();

impl Scopes {
    ident!(pub <usize, str>: [

        00 => "read",
        01 => "write",

        02 => "execute"

    ]);
}

// Go from A to B
assert_eq!(
    Scopes::ident_to(&0),
    Some("read")
);

// Go from B to A
assert_eq!(
    Scopes::ident_from("write"),
    Some(&1)
);

// Do nothing for undefined values
assert_eq!(
    Scopes::ident_to(&45),
    None
);