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*/ = // exposition only
!std::is_reference_v<T> && requires(T t) {
typename std::tuple_size<T>::type; // ensures std::tuple_size<T> is complete
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>>;
typename std::tuple_element_t<1, std::remove_const<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>&>;
}; |
(2) | (since C++20) |
template< class T, class U, class V > concept /*pair-like-convertible-from*/ = // exposition only !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>>; |
(3) | (since C++20) |
subrange to a pair-like type (i.e. a type models
pair-like, see below). Equivalent to
return PairLike(i_, s_);, where
i_ and
s_ are the stored iterator and sentinel respectively. This conversion function has additional constraints imposed by
pair-like-convertible (see below).
pair-like specifies a type is pair-like. Generally, an expression
e of a pair-like type can be used for
structured binding (i.e.
auto const& [x, y] = e; is generally well-formed). Like standard concepts, this concept is modeled if it is satisfied and all concepts it subsumes are modeled.
pair-like-convertible-from refines
pair-like. It rejects
range types and requires that
U and
V are convertible to the first and second element type of
T respectively, and the conversion from
U (which will be replaced by
const I&) to the first element type is non-slicing (see
convertible-to-non-slicing). Like standard concepts, this concept is modeled if it is satisfied and all concepts it subsumes are modeled.
The exposition only concept different-from is modeled by types T and U if and only if std::decay_t<T> and std::decay_t<U> are different types.
Parameters
(none).
Return value
A PairLike value direct-initialized with the stored iterator and sentinel.
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>
A program-defined type derived from one of these types or a std::variant specialization can be a pair-like type, if.
-
std::tuple_sizeandstd::tuple_elementare correctly specialized for it, and - calls to
std::get<0>andstd::get<1>for its value are well-formed.
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 legacy_strview = std::pair<
std::string::const_iterator,
std::string::const_iterator
>;
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
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