std::ranges...tor_closure(3)

okay so we're on the std::ranges...tor_closure(3) page from the C++ Standard Libary manual — yes, “Libary” is literally how the header spells it, don’t come for me 💀💅.

💖 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,
std::remove_cv_t<D>>

class range_adaptor_closure {};

(since C++23) — this is the C++23 era, bestie ✨

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 ✨

The page starts the example with // Run this code — here's the whole thing, no cap:

// 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");
}

mwah 💋 — source: http://cppreference.com; date: 2024.06.10. That's the footer, folded into this cute little sign-off 🫶