rvalue based copy

[matovitch via Digitalmars-d-learn]

On Monday, 30 March 2015 at 17:21:53 UTC, Steven Schveighoffer 
wrote:
  Annoying as this is (and blatantly awkward), it saves
> you from having to implement twice:
>
> void opAssign(T)(auto ref const T s) if(is(T == S)) {...}

Yep, this seems awkward to me too thought according to Adam one 
can do :

void opAssign()(auto ref const S s) {...}