std::ranges::views::as_const, std::ranges::as_const_view - cppreference.com (original) (raw)

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. 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.

Contents

• 1 Data members
• 2 Member functions
  • 2.1 Inherited from std::ranges::view_interface
• 3 std::ranges::as_const_view::as_const_view
  • 3.1 Parameters
• 4 std::ranges::as_const_view::base
• 5 std::ranges::as_const_view::begin
• 6 std::ranges::as_const_view::end
• 7 std::ranges::as_const_view::size
• 8 std::ranges::as_rvalue_view::reserve_hint
  • 8.1 Deduction guides
  • 8.2 Helper templates
  • 8.3 Notes
  • 8.4 Example
  • 8.5 See also

[edit] Data members

[edit] Member functions

std::ranges::as_const_view::as_const_view

| | (1) | (since C++23) | | | --------------------------------------------- | ------------- | ------------- | | constexpr explicit as_const_view( V base ); | (2) | (since C++23) |

1. Value-initializes _[base](#base)_ via its default member initializer (= V()).

2. Initializes _[base](#base)_ with std::move(base).

Parameters

std::ranges::as_const_view::base

| | (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](#base)_ ;.

2. Move-constructs the result from the underlying view. Equivalent to return std::move(_[base](#base)_ );.

std::ranges::as_const_view::begin

Returns the constant iterator of the view. Equivalent to return ranges::cbegin(_[base](#base)_ );.

std::ranges::as_const_view::end

Returns the constant sentinel of the view. Equivalent to return ranges::cend(_[base](#base)_ );.

std::ranges::as_const_view::size

Returns the size of the view if the view is bounded. Equivalent to return ranges::size(_[base](#base)_ );.

std::ranges::as_rvalue_view::reserve_hint

Returns ranges::reserve_hint(_[base](#base)_ ).

[edit] Deduction guides

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

[edit] Helper templates

This specialization of ranges::enable_borrowed_range makes as_const_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Notes

[edit] Example

#include #include   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 }

[edit] See also