std::basic_const_iterator<Iter>::operator constant-iterator

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std::basic_const_iterator
template < /*not-a-const-iterator*/ CI >

requires /*constant-iterator*/ <CI> &&
std::convertible_to <Iter const &, CI>

constexpr operator CI( ) const & ;
(1) (since C++23)
template < /*not-a-const-iterator*/ CI >

requires /*constant-iterator*/ <CI> &&
std::convertible_to <Iter, CI>

constexpr operator CI( ) && ;
(2) (since C++23)

Returns the converted constant iterator to which an underlying iterator current can be explicitly or implicitly convertible.

CI satisfies the exposition-only concept /*not-a-const-iterator*/ if and only if it's not a specialization of basic_const_iterator

Return value

1) current
2) std::move( current )

Example

Run this code
#include <iterator>
#include <ranges>
#include <vector>
 
void foo(std::vector<int>::const_iterator) {}
 
int main()
{
    auto v = std::vector<int>();
    {
        // ranges::cbegin below returns vector<int>::const_iterator
        auto i1 = std::ranges::cbegin(v);
        foo(i1); // okay
    }
 
    auto t = v | std::views::take_while([](int const x) { return x < 100; });
    {
        // ranges::cbegin below returns basic_const_iterator<vector<int>::iterator>
        auto i2 = std::ranges::cbegin(t);
        foo(i2); // error until P2836R1
    }
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2836R1 C++23 basic_const_iterator doesn't follow its underlying type's convertibility conversion operator provided
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