> 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
>
> I just wanted to make the connection between the two problems; and hopeful
> solve the has_operator and typeof_operator problem together.
The operator traits can detect if the operator return value can be
converted to a given type but not the precise return type.

what do you mean by "it can't"? is that a limitation of the language? or the library?
can't the built-in type cases by hard coded, e.g.

template<>
multiply_typeof_helper<double, int>{
typedef double type;
};

it can always be specialized, and for decltype compilers it can be by default:

template<class T1, class T2>
multiply_typeof_helper{
typedef decltype(T1()*T2()) type;
};

isn't this something that fits in type traits?

Alfredo