Difference between revisions of "cpp/ranges/as const view"
From cppreference.com
D41D8CD98F (Talk | contribs) (link to cpp/named req/RangeAdaptorObject) |
m (→See also: +`std::as_const`; fmt) |
||
| Line 1: | Line 1: | ||
| − | {{cpp/ranges/view title | as_const}} | + | {{cpp/ranges/view title|as_const}} |
{{cpp/ranges/navbar}} | {{cpp/ranges/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | ranges}} | + | {{dcl header|ranges}} |
| − | {{dcl | num=1 | since=c++23 |1= | + | {{dcl|num=1|since=c++23|1= |
template< ranges::view V > | template< ranges::view V > | ||
requires ranges::input_range<V> | requires ranges::input_range<V> | ||
| − | class as_const_view : public ranges::view_interface<as_const_view<V>> | + | class as_const_view |
| + | : public ranges::view_interface<as_const_view<V>> | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 |1= | + | {{dcl|num=2|since=c++23|1= |
namespace views { | namespace views { | ||
inline constexpr /* unspecified */ as_const = /* unspecified */; | inline constexpr /* unspecified */ as_const = /* unspecified */; | ||
| Line 14: | Line 15: | ||
}} | }} | ||
{{dcl h|Call signature}} | {{dcl h|Call signature}} | ||
| − | {{dcl | since=c++23 |1= | + | {{dcl|since=c++23|1= |
template< ranges::viewable_range R > | template< ranges::viewable_range R > | ||
requires /* see below */ | requires /* see below */ | ||
| Line 34: | Line 35: | ||
===Data members=== | ===Data members=== | ||
| − | Typical implementations of {{tt|as_const_view}} only hold one non-static data member: | + | Typical implementations of {{tt|as_const_view}} only hold one non-static data member: |
* the underlying view of type {{tt|V}} (shown here as {{tt|''base_''}}, the name is exposition only). | * the underlying view of type {{tt|V}} (shown here as {{tt|''base_''}}, the name is exposition only). | ||
===Member functions=== | ===Member functions=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc mem ctor | nolink=true | constructs an {{tt|as_const_view}} | notes={{mark c++23}} }} | + | {{dsc mem ctor|nolink=true|constructs an {{tt|as_const_view}}|notes={{mark c++23}}}} |
| − | {{dsc mem fun | nolink=true | base | returns the underlying view {{tt|V}} | notes={{mark c++23}} }} | + | {{dsc mem fun|nolink=true|base|returns the underlying view {{tt|V}}|notes={{mark c++23}}}} |
| − | {{dsc mem fun | nolink=true | begin | returns the beginning iterator of the {{tt|as_const_view}} | notes={{mark c++23}} }} | + | {{dsc mem fun|nolink=true|begin|returns the beginning iterator of the {{tt|as_const_view}}|notes={{mark c++23}}}} |
| − | {{dsc mem fun | nolink=true | end | returns the end iterator of the {{tt|as_const_view}} | notes={{mark c++23}} }} | + | {{dsc mem fun|nolink=true|end|returns the end iterator of the {{tt|as_const_view}}|notes={{mark c++23}}}} |
| − | {{dsc mem fun | nolink=true | size | returns the size of the view if it is bounded | notes={{mark c++23}} }} | + | {{dsc mem fun|nolink=true|size|returns the size of the view if it is bounded|notes={{mark c++23}}}} |
{{cpp/ranges/view_interface/inherit|embedded=yes|size=yes}} | {{cpp/ranges/view_interface/inherit|embedded=yes|size=yes}} | ||
{{dsc end}} | {{dsc end}} | ||
| − | {{member | {{small|std::ranges::as_const_view::}}as_const_view | | + | {{member|{{small|std::ranges::as_const_view::}}as_const_view| |
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | since=c++23 |1= | + | {{dcl|num=1|since=c++23|1= |
as_const_view() requires std::default_initializable<V> = default; | as_const_view() requires std::default_initializable<V> = default; | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 | | + | {{dcl|num=2|since=c++23| |
| − | constexpr explicit as_const_view(V base); | + | constexpr explicit as_const_view( V base ); |
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| Line 63: | Line 64: | ||
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | base | a view }} | + | {{par|base|a view}} |
{{par end}} | {{par end}} | ||
}} | }} | ||
| − | {{member | {{small|std::ranges::as_const_view::}}base| | + | {{member|{{small|std::ranges::as_const_view::}}base| |
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | since=c++23 | | + | {{dcl|num=1|since=c++23| |
constexpr V base() const& requires std::copy_constructible<V>; | constexpr V base() const& requires std::copy_constructible<V>; | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 | | + | {{dcl|num=2|since=c++23| |
constexpr V base() &&; | constexpr V base() &&; | ||
}} | }} | ||
| Line 82: | Line 83: | ||
}} | }} | ||
| − | {{member | {{small|std::ranges::as_const_view::}}begin| | + | {{member|{{small|std::ranges::as_const_view::}}begin| |
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | since=c++23 | | + | {{dcl|num=1|since=c++23| |
| − | constexpr auto begin() requires (! | + | constexpr auto begin() requires (!__simple_view<V>) { |
| − | + | return ranges::cbegin(base_); | |
} | } | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 | | + | {{dcl|num=2|since=c++23| |
| − | constexpr auto begin() const requires ranges::range<const V> { | + | constexpr auto begin() const requires ranges::range<const V> { |
| − | + | return ranges::cbegin(base_); | |
} | } | ||
}} | }} | ||
| Line 98: | Line 99: | ||
}} | }} | ||
| − | {{member | {{small|std::ranges::as_const_view::}}end| | + | {{member|{{small|std::ranges::as_const_view::}}end| |
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | since=c++23 | | + | {{dcl|num=1|since=c++23| |
| − | constexpr auto end() requires (! | + | constexpr auto end() requires (!__simple_view<V>) { |
| − | + | return ranges::cend(base_); | |
} | } | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 | | + | {{dcl|num=2|since=c++23| |
| − | constexpr auto end() const requires ranges::range<const V> { | + | constexpr auto end() const requires ranges::range<const V> { |
| − | + | return ranges::cend(base_); | |
} | } | ||
}} | }} | ||
| Line 114: | Line 115: | ||
}} | }} | ||
| − | {{member | {{small|std::ranges::as_const_view::}}size| | + | {{member|{{small|std::ranges::as_const_view::}}size| |
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | since=c++23 | | + | {{dcl|num=1|since=c++23| |
constexpr auto size() requires ranges::sized_range<V> { | constexpr auto size() requires ranges::sized_range<V> { | ||
return ranges::size(base_); | return ranges::size(base_); | ||
} | } | ||
}} | }} | ||
| − | {{dcl | num=2 | since=c++23 | | + | {{dcl|num=2|since=c++23| |
constexpr auto size() const requires ranges::sized_range<const V> { | constexpr auto size() const requires ranges::sized_range<const V> { | ||
return ranges::size(base_); | return ranges::size(base_); | ||
| Line 131: | Line 132: | ||
===Deduction guides=== | ===Deduction guides=== | ||
| − | {{ddcl | since=c++23 | | + | {{ddcl|since=c++23| |
| − | template<class R> | + | template< class R > |
| − | as_const_view(R&&) -> as_const_view<views::all_t<R>>; | + | as_const_view( R&& ) -> as_const_view<views::all_t<R>>; |
}} | }} | ||
===Helper templates=== | ===Helper templates=== | ||
{{ddcl|since=c++23|1= | {{ddcl|since=c++23|1= | ||
| − | template<class T> | + | template< class T > |
inline constexpr bool enable_borrowed_range<std::ranges::as_const_view<T>> = | inline constexpr bool enable_borrowed_range<std::ranges::as_const_view<T>> = | ||
std::ranges::enable_borrowed_range<T>; | std::ranges::enable_borrowed_range<T>; | ||
| Line 149: | Line 150: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/ranges/dsc cbegin}} | + | {{dsc inc|cpp/ranges/dsc cbegin}} |
| − | {{dsc inc | cpp/ranges/dsc cend}} | + | {{dsc inc|cpp/ranges/dsc cend}} |
| + | {{dsc inc|cpp/utility/dsc as_const}} | ||
<!-- | <!-- | ||
| − | {{dsc inc | cpp/iterator/dsc basic_const_iterator}} | + | {{dsc inc|cpp/iterator/dsc basic_const_iterator}} |
--> | --> | ||
{{dsc end}} | {{dsc end}} | ||
Revision as of 15:37, 18 January 2023
| Defined in header <ranges>
|
||
| template< ranges::view V > requires ranges::input_range<V> |
(1) | (since C++23) |
| 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) | |
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
Xand some extentExtentifUdenotes std::span<X, Extent>; - otherwise, ranges::ref_view(static_cast<const U&>(e)) if
eis an lvalue, const U modelsconstant_range, and U does not modelview. - 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 |
Expression-equivalent
Expression e is expression-equivalent to expression f, if
- e and f have the same effects, and
- either both are constant subexpressions or else neither is a constant subexpression, and
- either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).
Data members
Typical implementations of as_const_view only hold one non-static data member:
- the underlying view of type
V(shown here asbase_, the name is exposition only).
Member functions
| (constructor) (C++23) |
constructs an as_const_view (public member function) |
| base (C++23) |
returns the underlying view V (public member function) |
| begin (C++23) |
returns the beginning iterator of the as_const_view (public member function) |
| end (C++23) |
returns the end iterator of the as_const_view (public member function) |
| size (C++23) |
returns the size of the view if it is bounded (public member function) |
Inherited from std::ranges::view_interface | |
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>)
| |
| (C++23) |
returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
|
| (C++23) |
returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
|
| 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>)
| |
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>)
| |
returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
| |
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>)
| |
returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)
| |
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).Parameters
| base | - | a view |
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_);.
std::ranges::as_const_view::begin
| constexpr auto begin() requires (!__simple_view<V>) { return ranges::cbegin(base_); |
(1) | (since C++23) |
| constexpr auto begin() const requires ranges::range<const V> { return ranges::cbegin(base_); |
(2) | (since C++23) |
Returns the constant iterator of the view.
std::ranges::as_const_view::end
| constexpr auto end() requires (!__simple_view<V>) { return ranges::cend(base_); |
(1) | (since C++23) |
| constexpr auto end() const requires ranges::range<const V> { return ranges::cend(base_); |
(2) | (since C++23) |
Returns the constant sentinel of the view.
std::ranges::as_const_view::size
| constexpr auto size() requires ranges::sized_range<V> { return ranges::size(base_); |
(1) | (since C++23) |
| constexpr auto size() const requires ranges::sized_range<const V> { return ranges::size(base_); |
(2) | (since C++23) |
Returns the size of the view if the view is bounded.
Deduction guides
| template< class R > as_const_view( R&& ) -> as_const_view<views::all_t<R>>; |
(since C++23) | |
Helper templates
| template< class T > inline constexpr bool enable_borrowed_range<std::ranges::as_const_view<T>> = |
(since C++23) | |
This specialization of std::ranges::enable_borrowed_range makes as_const_view satisfy borrowed_range when the underlying view satisfies it.
Example
| This section is incomplete Reason: example |
See also
| (C++20) |
returns an iterator to the beginning of a read-only range (customization point object) |
| (C++20) |
returns a sentinel indicating the end of a read-only range (customization point object) |
| (C++17) |
obtains a reference to const to its argument (function template) |
