Macro impl_trait

macro_rules! impl_trait {
    (Hash for
     $(
        $type:ident<$($lt:lifetime),* $(,)? $($generic:ident),*>
        $(where $($bounded:ident),+ )?
     );+ |$self:ident, $state:ident| $expr:expr) => { ... };
    (Hash for $($type:ident),+ |$self:ident, $state:ident| $expr:expr) => { ... };
    (fmt::$trait:ident for
     $(
        $type:ident<$($lt:lifetime),* $(,)? $($generic:ident),*>
        $(where $($bounded:ident),+ )?
     );+ |$self:ident, $f:ident| $expr:expr) => { ... };
    (fmt::$trait:ident for $($type:ident),+ |$self:ident, $f:ident| $expr:expr) => { ... };
}

A helper macro to concisely implement a few common utility traits.

Traits supported

• Hash
• fmt:: Debug, Display…

Features:

• Allows multiple types in a single invocation, separated by semicolon
• Supports types with or without lifetimes and generics.
• Comma between lifetimes and generics is optional but recommended for clarity.
• Requires the same formatting trait (fmt::<trait>) to be implemented for all generics.

Example

struct S0(usize);
struct S1<T> { v: T }
struct S2<'a, T> { v: &'a T }

impl_trait![Hash for S0 |self, state| self.0.hash(state)];

impl_trait![fmt::Binary for S1<T> where T |self, f| self.v.fmt(f)];

impl_trait!{fmt::Debug for S1<T> where T; S2<'a, T> where T |self, f| {
    write!(f, "S? {{ v: {:?} }}", self.v)
}}