std::ranges...s_const_view(3)

🌈 NAME 🌈

Okay bestie, welcome to the std::ranges...s_const_view(3) page from the C++ Standard Libary 💖. The whole vibe is about std::ranges::views::as_const,std::ranges::as_const_view — yes, that comma is living its best life exactly like that, no notes.

std::ranges::views::as_const,std::ranges::as_const_view - std::ranges::views::as_const,std::ranges::as_const_view

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✨ Synopsis ✨

Defined in header <ranges> 🎀

template< ranges::view V >

    requires ranges::input_range<V>
(1) (since C++23)
class as_const_view

    : public ranges::view_interface<as_const_view<V>>
namespace views {

    inline constexpr /* unspecified */ as_const = /* unspecified
(2) (since C++23)
*/;

}
Call signature
template< ranges::viewable_range R >

    requires /* see below */
(since C++23)

constexpr ranges::view auto as_const( R&& r );

1. (1) A range adaptor that represents a view of underlying view that is also a constant_range. An as_const_view always has read-only elements (if not empty). 🔒
2. (2) RangeAdaptorObject. Let e be a subexpression, let T be decltype((e)), and let U be std::remove_cvref_t<T>. Then the expression views::as_const(e) is expression-equivalent to:
   • views::all(e), if it is a well-formed expression and views::all_t<T> models constant_range;
   • otherwise, std::span<const X, Extent>(e) for some type X and some extent Extent if U denotes std::span<X, Extent>;
   • otherwise, ranges::ref_view(static_cast<const X&>(e.base())) if U denotes ranges::ref_view<X> for some type X and const X models constant_range;
   • otherwise, ranges::ref_view(static_cast<const U&>(e)) if e is an lvalue, const U models constant_range, and U does not model view.
   • otherwise, as_const_view{e}.

as_const_view always models constant_range, and it models the contiguous_range, random_access_range, bidirectional_range, forward_range, borrowed_range, common_range, and sized_range when the underlying view V models respective concepts. Slay 💅

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💅 Member functions 💅

• constructor — constructs an as_const_view (public member function)
• base — returns the underlying view V (public member function)
• begin — returns the beginning iterator of the as_const_view (public member function)
• end — returns the end iterator of the as_const_view (public member function)
• size — returns the size of the view if it is bounded (public member function)

🎀 Inherited from std::ranges::view_interface 🎀

• empty (C++20) — returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function of std::ranges::view_interface<D>)
• cbegin (C++23) — returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
• cend (C++23) — returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
• operator bool (C++20) — returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
• data (C++20) — gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function of std::ranges::view_interface<D>)
• front (C++20) — returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
• back (C++20) — returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>)
• operator[] (C++20) — returns the n^th element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

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🌟 std::ranges::as_const_view::as_const_view 🌟

as_const_view() requires std::default_initializable<V> = default; (1) (since C++23)
constexpr explicit as_const_view( V base );                       (2) (since C++23)

1. Value-initializes base_ via its default member initializer (= V()).
2. Initializes base_ with std::move(base).

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🍓 Parameters 🍓

• base — a view

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🌸 std::ranges::as_const_view::base 🌸

constexpr V base() const& requires std::copy_constructible<V>; (1) (since C++23)
constexpr V base() &&;                                         (2) (since C++23)

Returns the underlying view.

1. Copy-constructs the result from the underlying view. Equivalent to return base_;.
2. Move-constructs the result from the underlying view. Equivalent to return std::move(base_);.

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🦋 std::ranges::as_const_view::begin 🦋

constexpr auto begin() requires (!__simple_view<V>);          (1) (since C++23)
constexpr auto begin() const requires ranges::range<const V>; (2) (since C++23)

Returns the constant iterator of the view.

1,2) Equivalent to return ranges::cbegin(base_);

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🧚 std::ranges::as_const_view::end 🧚

constexpr auto end() requires (!__simple_view<V>);          (1) (since C++23)
constexpr auto end() const requires ranges::range<const V>; (2) (since C++23)

Returns the constant sentinel of the view.

1,2) Equivalent to return ranges::cend(base_);

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⭐ std::ranges::as_const_view::size ⭐

constexpr auto size() requires ranges::sized_range<V>;       (1) (since C++23)
constexpr auto size() const requires ranges::sized_range<const V>; (2) (since C++23)

Returns the size of the view if the view is bounded.

1,2) Equivalent to return ranges::size(base_);

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🧚 Deduction guides 🧚

template< class R >                                      (since C++23)
as_const_view( R&& ) -> as_const_view<views::all_t<R>>;

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🎀 Helper templates 🎀

template< class T >

inline constexpr bool
enable_borrowed_range<std::ranges::as_const_view<T>>   (since
    =
C++23)

    std::ranges::enable_borrowed_range<T>;

This specialization of std::ranges::enable_borrowed_range makes as_const_view satisfy borrowed_range when the underlying view satisfies it. Bestie, that's the whole point 💖

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📝 Notes 📝

Feature-test macro realness:

• Feature-test macro: __cpp_lib_ranges_as_const
• Value: 202207L
• Std: (C++23)
• Feature: std::ranges::as_const_view, std::const_iterator

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🔥 Example 🔥

// Run this code

#include <cassert>
#include <ranges>

int main()
{
    int x[]{1, 2, 3, 4, 5};

    auto v1 = x | std::views::drop(2);
    assert(v1.back() == 5);
    v1[0]++; // OK, can modify non-const element

    auto v2 = x | std::views::drop(2) | std::views::as_const;
    assert(v2.back() == 5);
    // v2[0]++; // Compile-time error, cannot modify read-only element
}

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👀 See also 👀

• ranges::as_rvalue_view — a view of a sequence that casts each element to an rvalue; views::as_rvalue — (class template) (range adaptor object); (C++23)
• ranges::cbegin — returns an iterator to the beginning of a read-only range; (customization point object); (C++20)
• ranges::cend — returns a sentinel indicating the end of a read-only range; (customization point object); (C++20)
• as_const — obtains a reference to const to its argument; (function template); (C++17)
• basic_const_iterator — iterator adaptor that converts an iterator into a constant iterator; (class template); (C++23)

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mwah 💋 — source: http://cppreference.com, version/date: 2024.06.10, and the page is std::ranges...s_const_view(3). Periodt. 🌈