Using iterator_traits to deduce value type from pair of iterators

Question

I have a type

typedef std::pair<ConstIterator, ConstIterator> Range;

with

typedef typename std::vector<T>::const_iterator ConstIterator;

I would now like to use std::iterator_traits to deduce the type the iterators of a Range are pointing to.

Could anybody please tell me how I can achieve this, from an object of type Range?

Answer 1

You can write a type trait, partially specialized on a pair:

template <typename T>
struct value_type {
    using type = typename std::iterator_traits<T>::value_type;
};

template <typename T>
struct value_type<std::pair<T, T>>
: value_type<T>
{ };