Macro forward_ref_generic::commutative_binop

macro_rules! commutative_binop {
    (
        $( [ $($generic:tt)* ] )?
        impl Add for $lhs:ty, $rhs:ty
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl Mul for $lhs:ty, $rhs:ty
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl $impl:ident, $meth:ident for $lhs:ty, $rhs:ty
        $( where $($bound:tt)* )?
    ) => { ... };
}

For types T, U for which binary operator binop is implemented (T binop U), also implement U binop T. This macro will fail if LHS = RHS.

For readability, the expected syntax of the macro is the following:

( [ Generics ] )?
impl Trait, Method for LHS(, RHS)?
( where Bounds )?

• Generics are comma-seperated type or const generics
• Trait is the trait to be implemented
• Method is the method that Trait defines
  (can be ommitted for Add and Mul)
• LHS is the type of the left hand side of the original operation (i.e. T)
• RHS is the type of the right hand side of the original operation (i.e. U)
• Bounds are comma-seperated trait bounds for the listed generics

Note in particular that LHS and RHS denote the left and right side of the original operation, not the one being created. The reason for this is to be consistent with all other macros in this crate, even if it seems unintuitive.