std::iterator_traits<std::counted_iterator>

Since C++20

Header: <iterator>

Inherits the properties from customized (generated from either a standard partial specialization or a program-defined specialization) std::iterator_traits, with the member type pointer adjusted, where I models input_iterator.

# Declarations

template< std::input_iterator I >
requires /* see below */
struct iterator_traits<std::counted_iterator<I>> : std::iterator_traits<I> {
using pointer = std::conditional_t<std::contiguous_iterator<I>,
std::add_pointer_t<std::iter_reference_t<I>>,
void>;
};

(since C++20)

# Example

#include <iterator>
#include <list>
#include <type_traits>
#include <vector>
 
int main()
{
    std::vector v{1, 2, 3, 4};
    std::list l{1, 2, 3, 4};
    std::counted_iterator iv{v.begin(), 3};
    std::counted_iterator il{l.begin(), 3};
    static_assert(std::is_same<int*, std::iterator_traits<decltype(iv)>::pointer>());
    static_assert(std::is_same<void, std::iterator_traits<decltype(il)>::pointer>());
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
P2259R1	C++20	there’s no requires-clausepointer is unconditionally defined as void	constraint added

# See also

iterator_traits