impl traits for enums

It is very common to implement traits for enums if all of its variants have implemented the traits.

#![allow(unused)]
fn main() {
enum Data {
    Bin( Vec<u8> ),
    Text( String ),
}

impl AsRef<[u8]> for Data {
    fn as_ref( &self ) -> &[u8] {
        match self {
            Data::Bin(  v ) => v.as_ref(),
            Data::Text( v ) => v.as_ref(),
        }
    }
}
}

In case of generic enums:

#![allow(unused)]
fn main() {
impl<T0,T1> AsRef<[u8]> for Enum2<T0,T1>
    where T0: AsRef<[u8]> 
        , T1: AsRef<[u8]> 
{
    fn as_ref( &self ) -> &[u8] {
        match self {
            Enum2::_0( s ) => s.as_ref(),
            Enum2::_1( s ) => s.as_ref(),
        }
    }
}
}

The basic idea is to match the variants and delegate. This library provides macros to help to avoid writing these boilerplate code:

1. The contextual macros

These macros helps not repeating the where clauses and match arms of each variant.

2. The predefined macros

These macros helps to omit the methods in impl blocks.