25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

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.

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

(2.1)

If views::all_t models constant_range, then views::all(E).
(2.2)

Otherwise, if U denotes empty_view for some type X, then auto(views::empty).
(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 for some type X andconst 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, andU 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 hammer = {'m', 'c'}; span beat = hammer; cant_touch_this(views::as_const(beat)); // will not modify the elements of hammer â end example]