I just want to make the connection with the thread I opened last week: "[math][tools][units] generic libraries not generic enough"

The point I want to make is that if there were a uniform facility to deduce the result of a built-in operator over some arithmetic types then library authors could do a better job at writting generic libraries on some exotic arithmetic types and combinations, for example

multiply_typeof_helper<double, int>::type --> double

the name is of course borrowed from boost.Units were it is intesively used:

boost::unit::multiplies_typeof_helper<quantity<si::length>, quantity<si::length> >::type --> quantity<si::area>

I just wanted to make the connection between the two problems; and hopeful solve the has_operator and typeof_operator problem together.

Alfredo
PS: what if to types can not be multiplied, etc, the has_multiplies will tell or multiplies_typeof_helper can return void, or boost::none.