Is there any reason except forgetfulness/"no time" that the old algorithms in

For example, std::shuffle does accept its random number generator by universal reference.

It would seem like a good idea and non-breaking to change the prototypes of any algorithm accepting a predicate to accept its functor by universal reference, or am I missing something.

I also can't seem to find a proposal suggesting this, nor a defect report about it being forgotten for ... C++11. Does anyone know more about this?

As a small/tiny example that shows a case where using forwarding references over functor by value: http://ift.tt/2BnBVdH.