Difference between std::result_of and decltype

Question

I have some trouble understanding the need for std::result_of in C++0x. If I understood correctly, result_of is used to obtain the resulting type o

Answer 1

result_of was introduced in Boost, and then included in TR1, and finally in C++0x. Therefore result_of has an advantage that is backward-compatible (with a suitable library).

decltype is an entirely new thing in C++0x, does not restrict only to return type of a function, and is a language feature.

---

Anyway, on gcc 4.5, result_of is implemented in terms of decltype:

  template
    class result_of;

  template
    struct result_of<_Functor(_ArgTypes...)>
    {
      typedef
        decltype( std::declval<_Functor>()(std::declval<_ArgTypes>()...) )
        type;
    };