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

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C++
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
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Range access
(C++11) (C++14)
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(C++11) (C++14)
(C++14) (C++14)
(C++17) (C++20)
(C++17)
(C++17)
std::basic_const_iterator
Member functions
basic_const_iterator::operator constant-iterator
Non-member functions
(C++23) (C++23) (C++23) (C++23)
(C++23)
(C++23)
(C++23)
Helper classes
(C++23)
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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