From cppreference.com
template</*not-a-const-iterator*/CI>requires/*constant-iterator*/<CI>&&std::convertible_to<Iterconst&,CI>constexproperatorCI()const&; (1) (since C++23)template</*not-a-const-iterator*/CI>requires/*constant-iterator*/<CI>&&std::convertible_to<Iter,CI>constexproperatorCI()&&; (2) (since C++23)Returns the converted constant iterator to which an underlying iterator
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
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#include<iterator>#include<ranges>#include<vector>voidfoo(std::vector<int>::const_iterator){}intmain(){autov=std::vector<int>();{// ranges::cbegin below returns vector<int>::const_iteratorautoi1=std::ranges::cbegin(v);foo(i1);// okay}autot=v|std::views::take_while([](intconstx){returnx<100;});{// ranges::cbegin below returns basic_const_iterator<vector<int>::iterator>autoi2=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
C++23 basic_const_iterator doesn't follow its underlying type's convertibility conversion operator provided