std::ranges::subrange<I,S,K>:: operator PairLike

template< class T >
concept /*pair-like*/ =
    !std::is_reference_v<T> && requires(T t)
    {
        typename std::tuple_size<T>::type;
        requires std::derived_from<std::tuple_size<T>,
                                   std::integral_constant<std::size_t, 2>>;
        typename std::tuple_element_t<0, std::remove_const_t<T>>;
        typename std::tuple_element_t<1, std::remove_const_t<T>>;
        { std::get<0>(t) } -> std::convertible_to<
                                  const std::tuple_element_t<0, T>&>;
        { std::get<1>(t) } -> std::convertible_to<
                                  const std::tuple_element_t<1, T>&>;
    };

template< class T, class U, class V >
concept /*pair-like-convertible-from*/ =
    !ranges::range<T> && /*pair-like*/<T> &&
    std::constructible_from<T, U, V> &&
    /*convertible-to-non-slicing*/<U, std::tuple_element_t<0, T>> &&
    std::convertible_to<V, std::tuple_element_t<1, T>>;

template< class T, class U, class V >
concept /*pair-like-convertible-from*/ =
    !ranges::range<T> && !std::is_reference_v<T> && /*pair-like*/<T> &&
    std::constructible_from<T, U, V> &&
    /*convertible-to-non-slicing*/<U, std::tuple_element_t<0, T>> &&
    std::convertible_to<V, std::tuple_element_t<1, T>>;

Return value

PairLike ( begin_  , end_  )

Notes

Following types in the standard library are pair-like:

• std:: pair < T, U >
• std:: tuple < T, U >
• std:: array < T, 2 >
• std :: ranges:: subrange < I, S, K >

Since subrange specializations are range types, conversion to them are not performed via this conversion function.

std::array specializations cannot be converted from subrange , since they are range types.

Example

#include <iostream>
#include <ranges>
#include <string>
#include <utility>
 
using striter = std::string::const_iterator;
 
using legacy_strview = std::pair<striter, striter>;
 
void legacy_print(legacy_strview p)
{
    for (; p.first != p.second; ++p.first)
        std::cout << *p.first << ' ';
    std::cout << '\n';
}
 
int main()
{
    std::string dat{"ABCDE"};
    for (auto v{std::ranges::subrange{dat}}; v; v = {v.begin(), v.end() - 1})
    {
        /*...*/
        legacy_print(legacy_strview{v});
    }
}

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A B C D 
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A

See also