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

template< /different-from/<subrange> PairLike > requires /pair-like-convertible-from/<PairLike, const I&, const S&> constexpr operator PairLike() const;	(1)	(since C++20)
Helper concepts
template< class T > concept /pair-like/ = /* see description */;	(2)	(exposition only*)
template< class T, class U, class V > concept /pair-like-convertible-from/ = /* see description */;	(3)	(exposition only*)

1) Converts subrange to a pair-like type.

For the definition of /*different-from*/, see different-from .

2) Determines whether a type is pair-like .

Equivalent to:

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>&>;
    };

(until C++23)

This concept is equivalent to the library-wide exposition-only concept pair-like.

(since C++23)

3) Determines whether a pair-like type can be constructed from two values of possibly different given types.

Equivalent to:

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>>;

(until C++23)

Equivalent to:

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>>;

(since C++23)

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>

std::complex<T>

(since C++26)

A program-defined type derived from one of these types can be a pair-like type, if

std::tuple_size and std::tuple_element are correctly specialized for it, and
calls to std::get<0> and std::get<1> for its value are well-formed.

(until C++23)

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});
    }
}

Output:

A B C D E 
A B C D 
A B C 
A B 
A

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

Return value

Notes

Example

See also