Question

Is it possible to specialize an Iterator template parameter by its value_type?

I have a function with the following prototype.

template<typename InputIterator>
void f(InputIterator first, InputIterator last);

And I want to handle specially if InputIterator::value_type is SomeSpecificType.

Answer 1

You can use some intermediate structs to get the partial template specialisation that you need. Something like this should do the trick

template<typename T, typename V>
struct f_impl
{
  static void f( T first, T last ) {...}; //Default version
};

template<typename T>
struct f_impl<T, SomeSpecificType>
{
   static void f(T first,T last) {...}; //Specialisation
};

template<typename InputIterator> void f(InputIterator first, InputIterator last)
{
  f_impl<
      InputIterator,
      typename std::iterator_traits<InputIterator>::value_type
  >::f(first,last);
};