Macro forward_ref_op_assign 

macro_rules! forward_ref_op_assign {
    (
        $( [ $($generic:tt)* ] )?
        impl AddAssign for $lhs:ty $(, $rhs:ty )?
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl SubAssign for $lhs:ty $(, $rhs:ty )?
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl MulAssign for $lhs:ty $(, $rhs:ty )?
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl DivAssign for $lhs:ty $(, $rhs:ty )?
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl $impl:ident, $meth:ident for $lhs:ty
        $( where $($bound:tt)* )?
    ) => { ... };
    (
        $( [ $($generic:tt)* ] )?
        impl $impl:ident, $meth:ident for $lhs:ty, $rhs:ty
        $( where $($bound:tt)* )?
    ) => { ... };
}

For types T: Copy, U: Copy for which assignment operator assop is implemented (T assop U), also implement T assop &U.

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 AddAssign, SubAssign, MulAssign and DivAssign)
• LHS is the type of the left hand side of the operation (i.e. T)
• RHS is the type of the right hand side of the operation (i.e. U)
  if no RHS is given, LHS = RHS is assumed
• Bounds are comma-seperated trait bounds for the listed generics