“Overload” function template based on function object operator() signature in C++98

Question

I want to make a template function that takes a function and a vector and uses the function to map that vector to another vector that will be returned by the function templa

Answer 1

Here's my approach:

template  struct ignore_value {typedef T type;};

template 
T& declval();

template
typename ignore_value()(declval())),
       std::vector >::type map_vec(F fnc, const std::vector& source);

template
typename ignore_value()
                         (declval(), declval >())),
       std::vector >::type map_vec(F fnc, const std::vector& source);

It works with the same Demo that 0x499602D2 used, with both GCC and Clang in C++98 mode.