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std::ranges::range_adaptor_closure

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)

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

#include <iostream>
#include <ranges>
#include <string>
#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;
 
    std::string_view operator()(std::string_view sv) const {
        return sv.substr(start, end - start);
    }
};
 
int main() {
    std::string str = "01234567";
 
    Slice slicer{.start = 1, .end = 6};
 
    auto sv1 = slicer(str);  // use slicer as a normal function object
    auto sv2 = str | slicer; // use slicer as a range adaptor closure object
    std::cout << sv1 << '\n';
    std::cout << sv2 << '\n';
 
    // range adaptor closures can be composed
    auto slice_and_drop = slicer
                        | std::views::drop_while([](auto ch) { return ch != '3'; });
    std::cout << std::string_view(str | slice_and_drop) << '\n';
}

Output:

12345
12345
345

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