std::ranges::range_adaptor_closure

template< class D >
requires std::is_object_v<D> && std::same_as<D, std::remove_cv_t<D>>
class range_adaptor_closure {};

#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};
 
    // use slicer as a normal function object
    constexpr auto sv1 = slicer(str);
    static_assert(sv1 == "12345");
 
    // use slicer as a range adaptor closure object
    constexpr auto sv2 = str | slicer;
    static_assert(sv2 == "12345");
 
    // range adaptor closures can be composed
    constexpr auto slice_and_drop = slicer | std::views::drop(2);
    static_assert(std::string_view(str | slice_and_drop) == "345");
}