Question

I would like to write a template that would get as a parameter the return type of the function in which it is being instantiated.

For example, assume I’ve a Result templated class:

template<type T>
class Result {
    T _result_value;
    T& operator=( T that );
    ~Result( );
}

There would be several specializations for this class. In the destructor I would like to log the return type, and within the operator= assignment I would like to check and assert for error values.

Ideally, I would like to be able to have such a define:

#define RESULT Result< /* decltype magic for type of current function */ >

so I could use it:

HFILE MyOpenFile( ... ) {
    RESULT result;
}

…which will be deduced to Result<HFILE>. This is a simplified example: writing RESULT instead of Result<HFILE> isn’t a big deal, but there are other scenarios where the return type of the current function isn’t easily obtained.

Answer 1

No. There’s nothing in C++ which refers to the “current function”. The closest is __func__ but that’s a string literal. Hence, there’s nothing to pass to decltype.

Not that you need it, with auto.