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std::ranges::range_adaptor_closure

From cppreference.com
< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)

Range primitives



Dangling iterator handling
Range concepts
Views

Range factories
Range adaptors
Range generators
Range adaptor objects
Range adaptor closure objects
range_adaptor_closure
(C++23)
Helper items
(until C++23)(C++23)


 
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.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_ranges 202202L (C++23) std::ranges::range_adaptor_closure

[edit] Example

#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");
}