std::ranges::range_adaptor_closure(3)

NAME
std::ranges::range_adaptor_closure - std::ranges::range_adaptor_closure

Synopsis
   Defined in header <ranges>
   template< class D >
       requires std::is_object_v<D> && std::same_as<D, (since C++23)
   std::remove_cv_t<D>>
   class range_adaptor_closure {};
   std::ranges::range_adaptor_closure is a helper class template for defining a
   RangeAdaptorClosureObject.
   Let t be the object of type T, the implementation ensures that t is a range adaptor
   closure object if all the requirements are met:
     * t is a unary function object that takes one range argument.
     * T has exactly one public base class ranges::range_adaptor_closure<T>, and T has
       no base classes of type ranges::range_adaptor_closure<U> for any other type U.
     * T does not satisfy range.

Example
// Run this code
 #include <ranges>
 #include <string_view>
 // Define Slice as a range adaptor closure
 struct Slice : std::ranges::range_adaptor_closure<Slice>
 {
     std::size_t start = 0;
     std::size_t end = std::string_view::npos;
     constexpr std::string_view operator()(std::string_view sv) const
     {
         return sv.substr(start, end - start);
     }
 };
 int main()
 {
     constexpr std::string_view str = "01234567";
     constexpr Slice slicer{.start = 1, .end = 6};
     constexpr auto sv1 = slicer(str); // use slicer as a normal function object
     constexpr auto sv2 = str | slicer; // use slicer as a range adaptor closure object
     static_assert(sv1 == "12345");
     static_assert(sv2 == "12345");
     // range adaptor closures can be composed
     constexpr auto slice_and_drop
         = slicer
         | std::views::drop_while([](char ch) { return ch != '3'; });
     static_assert(std::string_view(str | slice_and_drop) == "345");
 }