[range.as.const]

26.7.21.1 Overview [range.as.const.overview]

as_const_view presents a view of an underlying sequence as constant.

That is, the elements of an as_const_view cannot be modified.

The name views::as_const denotes a range adaptor object ([range.adaptor.object]).

Let E be an expression, let T be decltype((E)), and let U be remove_cvref_t<T>.

The expression views::as_const(E) is expression-equivalent to:

(2.1)
If views::all_t<T> models constant_range, then views::all(E).
(2.2)
Otherwise, if U denotes empty_view<X> for some type X, then auto(views::empty<const X>).
(2.3)
Otherwise, if U denotes span<X, Extent> for some type X and some extent Extent, then span<const X, Extent>(E).
(2.4)
Otherwise, if U denotes ref_view<X> for some type X and const X models constant_range, then ref_view(static_cast<const X&>(E.base())).
(2.5)
Otherwise, if E is an lvalue, const U models constant_range, and U does not model view, then ref_view(static_cast<const U&>(E)).
(2.6)
Otherwise, as_const_view(E).

[Example 1: template<constant_range R> void cant_touch_this(R&&); vector<char> hammer = {'m', 'c'}; span<char> beat = hammer; cant_touch_this(views::as_const(beat)); // will not modify the elements of hammer — end example]

26.7.21.2 Class template as_const_view [range.as.const.view]

namespace std::ranges { template<view V> requires input_range<V> class as_const_view : public view_interface<as_const_view<V>> { V base_ = V(); // exposition only public: as_const_view() requires default_initializable<V> = default; constexpr explicit as_const_view(V base); constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() requires (!simple-view<V>) { return ranges::cbegin(base_); } constexpr auto begin() const requires range<const V> { return ranges::cbegin(base_); } constexpr auto end() requires (!simple-view<V>) { return ranges::cend(base_); } constexpr auto end() const requires range<const V> { return ranges::cend(base_); } constexpr auto size() requires sized_range<V> { return ranges::size(base_); } constexpr auto size() const requires sized_range<const V> { return ranges::size(base_); } }; template<class R> as_const_view(R&&) -> as_const_view<views::all_t<R>>; }

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constexpr explicit as_const_view(V base);

Effects: Initializes base_ with std::move(base).

26 Ranges library [ranges]

26.7 Range adaptors [range.adaptors]

26.7.21 As const view [range.as.const]

26.7.21.1 Overview [range.as.const.overview]

26.7.21.2 Class template as_const_view [range.as.const.view]