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357 lines
7.3 KiB
Markdown
357 lines
7.3 KiB
Markdown
---
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title: "array_view"
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---
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{{< callout >}}
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Header: `array_view.h`
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Since: All versions
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Similar to: [gsl::array_view](https://learn.microsoft.com/en-us/previous-versions/cpp/parallel/amp/reference/array-view-class)
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{{< /callout >}}
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This class implements a view in to a range of a C array, `etl::array`, `std::array`, `etl::vector` and `std::vector`.
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It will support construction from any class that supports data() and size() member functions as well as plain C arrays.
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If `ETL_ARRAY_VIEW_IS_MUTABLE` is defined, then the contents of the view are mutable.
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The view is non-mutable by default, which is the opposite to the behaviour in 17.5.0 or earlier.
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```cpp
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etl::array_view<typename T>
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```
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## Template deduction guides
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**C++17 and above**
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```cpp
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template <typename TArray>
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etl::array_view(TArray& a)
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-> etl::array_view<typename TArray::value_type>;
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```
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```cpp
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template <typename TIterator>
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etl::array_view(const TIterator begin_, const TIterator end_)
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-> etl::array_view<etl::remove_pointer_t<TIterator>>;
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```
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```cpp
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template <typename TIterator, typename TSize>
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etl::array_view(const TIterator begin_, const TSize size_)
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-> etl::array_view<etl::remove_pointer_t<TIterator>>;
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```
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## Examples
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```cpp
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etl::array data{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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etl::array_view view1{ data };
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etl::array_view view2{ data.begin(), data.end() };
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etl::array_view view3{ data.begin(), data.size() };
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etl::array_view view4{ view1 };
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```
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## Member types
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`value_type`
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`size_type`
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`difference_type`
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`reference`
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`const_reference`
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`pointer`
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`const_pointer`
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`iterator`
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`const_iterator`
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`reverse_iterator`
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`const_reverse_iterator`
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## Constructors
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```cpp
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ETL_CONSTEXPR array_view()
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```
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**Description**
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Default constructor.
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---
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```cpp
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template <typename TArray>
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ETL_CONSTEXPR explicit array_view(TArray& a)
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```
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**Description**
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Construct from array or vector like class.
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---
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```cpp
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template <typename TIterator>
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ETL_CONSTEXPR array_view(TIterator begin_, TIterator end_)
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```
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**Description**
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Construct from an iterator or pointer range.
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---
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```cpp
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template <typename TIterator, typename TSize>
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ETL_CONSTEXPR array_view(TIterator begin_, TSize size_)
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```
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**Description**
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Construct from a start and size
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---
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```cpp
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template<const size_t ARRAY_SIZE>
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ETL_CONSTEXPR explicit array_view(T(&begin_)[ARRAY_SIZE])
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```
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**Description**
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Construct from a compile time sized C array.
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---
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```cpp
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ETL_CONSTEXPR array_view(const array_view& other)
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```
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**Description**
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Copy constructor.
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## Modifiers
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```cpp
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template <typename TIterator>
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void assign(TIterator begin_, TIterator end_)
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```
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**Description**
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Assigns begin and end of the supplied range.
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Does not copy the elements in the range.
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---
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```cpp
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template <typename TIterator, typename TSize>
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void assign(TIterator begin_, TSize size_)
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```
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**Description**
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Assign from a start iterator and length.
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Does not copy the elements in the range.
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---
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```cpp
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void remove_prefix(size_type n)
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```
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**Description**
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Shrinks the view from the front.
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A value of `n` larger than the array will result in undefined behaviour.
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---
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```cpp
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void remove_suffix(size_type n)
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```
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**Description**
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Shrinks the view from the back.
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A value of `n` larger than the array will result in undefined behaviour.
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---
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```cpp
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void fill(value_type value)
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```
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*Introduced:* `20.24.0`
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**Description**
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Fill the underlying array with value.
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## Element access
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Mutable access is only possible by defining the macro `ETL_ARRAY_VIEW_IS_MUTABLE`.
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In this case, `reference`, `pointer`, `iterator` and `reverse_iterator` are defined as their `const` counterparts.
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```cpp
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reference at(size_t i)
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const_reference at(size_t i) const
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```
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**Description**
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Gets a reference or const reference to the indexed element.
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Emits an `etl::array_view_uninitialised` if the view is not initialised.
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Emits an `etl::array_view_bounds` if the index is not in range.
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If asserts or exceptions are not enabled then undefined behaviour occurs.
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**Parameters**
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`i` The index.
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**Returns**
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A reference or const reference to the indexed element
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---
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```cpp
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reference operator[](size_t i)
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const_reference operator[](size_t i) const
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```
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**Description**
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Gets a reference or const reference to the indexed element.
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**Returns**
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A reference or const reference to the indexed element.
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Undefined behaviour if the `array_view` is empty.
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---
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```cpp
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reference front()
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const_reference front() const
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```
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**Description**
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Gets a reference or const reference to the first element.
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**Returns**
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A reference or const reference to the first element.
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Undefined behaviour if the `array_view` is empty.
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---
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```cpp
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reference back()
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const_reference back() const
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```
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**Description**
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Gets a reference or const reference to the last element.
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**Returns**
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A reference or const reference to the last element.
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Undefined behaviour if the `array_view` is empty.
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---
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```cpp
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pointer data()
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const_pointer data() const
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```
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**Description**
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Gets a pointer or const pointer to the first element.
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**Returns**
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A pointer or const pointer to the first element.
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Equal to `end()` if the array_view is empty.
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## Iterators
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```cpp
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iterator begin()
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const_iterator begin() const
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const_iterator cbegin() const
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```
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**Description**
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Returns an iterator to the beginning of the array view.
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---
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```cpp
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iterator end()
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const_iterator end() const
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const_iterator cend() const
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```
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**Description**
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Returns an iterator to the end of the array view.
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---
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```cpp
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iterator rbegin()
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const_iterator rbegin() const
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const_iterator crbegin() const
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```
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**Description**
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Gets a reverse iterator to the beginning of the array view.
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---
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```cpp
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iterator rend()
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const_iterator rend() const
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const_iterator crend() const
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```
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**Description**
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Gets a reverse iterator to the end of the array view.
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---
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Capacity
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```cpp
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bool empty() const
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```
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**Description**
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Returns true if the size of the array view is zero, otherwise false.
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---
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```cpp
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size_t size() const
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```
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**Description**
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Returns the size of the view.
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---
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```
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C++size_t max_size() const
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```
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**Description**
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Returns the maximum possible size of the view.
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---
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## Non-member functions
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**Lexicographically comparisons**
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`operator ==`
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**Returns**
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Returns `true` if the contents of the array views are equal, otherwise `false`.
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---
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`operator !=`
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**Returns**
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`true` if the contents of the array views are not equal, otherwise `false`.
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`operator <`
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**Returns**
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`true` if the contents of the lhs are lexicographically less than the
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contents of the rhs, otherwise `false`.
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`operator <=`
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**Returns**
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`true` if the contents of the lhs are lexicographically less than or equal to the
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contents of the rhs, otherwise `false`.
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`operator >`
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**Returns**
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`true` if the contents of the lhs are lexicographically greater than the
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contents of the rhs, otherwise `false`.
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`operator >=`
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**Returns**
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`true` if the contents of the lhs are lexicographically greater than or equal to the
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contents of the rhs, otherwise `false`.
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## Hash
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There are specialisations of `etl::hash` for `array_view`.
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## Example
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```cpp
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etl::array<int, 10> data = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
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typedef etl::array_view<int> View;
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View view(data.begin() + 2, data.end() - 2);
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void Print(const View& view)
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{
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for (size_t i = 0; i < view.size(); ++i)
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{
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std::cout << view[i] << " ";
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}
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}
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Print(view); // Prints "3 4 5 6 7 8"
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size_t hashvalue = etl::hash<View>()(view);
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``` |