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411 lines
8.4 KiB
Markdown
411 lines
8.4 KiB
Markdown
---
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title: "span"
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---
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{{< callout >}}
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Header: `span.h`
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Similar to: `std::span`
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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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Since: `20.34.0`
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The ETL's span adds the ability to access circular iterators that will loop through the span when the beginning or end is reached.
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```cpp
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etl::span<typename T, size_t Extent = etl::dynamic_extent>
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```
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## Template deduction guides
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C++17
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```cpp
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template <typename TIterator>
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span(const TIterator begin, const TIterator end)
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->span<etl::remove_pointer_t<TIterator>, etl::dynamic_extent>;
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```
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```cpp
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template <typename TIterator, typename TSize>
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span(const TIterator begin, const TSize size)
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->span<etl::remove_pointer_t<TIterator>, etl::dynamic_extent>;
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```
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```cpp
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template <typename T, size_t N>
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span(T(&)[N])
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-> span<T, N>;
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```
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```cpp
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template <typename T, size_t N>
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span(etl::array<T, N>&)
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-> span<T, N>;
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```
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```cpp
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template <typename T, size_t N>
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span(const etl::array<T, N>&)
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-> span<const T, N>;
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```
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```cpp
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template <typename T, size_t N>
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span(std::array<T, N>&)
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->span<T, N>;
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```
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```cpp
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template <typename T, size_t N>
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span(const std::array<T, N>&)
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->span<const T, N>;
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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::span span1{ data };
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etl::span span2{ data.begin(), data.end() };
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etl::span span3{ data.begin(), data.size() };
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etl::span span4{ span1 };
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int c_array[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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etl::span span5{ c_array };
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```
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## Member types
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```cpp
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element_type T
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value_type remove_cv<T>::type
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size_type size_t
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difference_type ptrdiff_t
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reference value_type&
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const_reference const value_type&
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pointer value_type*
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const_pointer const value_type*
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iterator A random access iterator
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reverse_iterator A reverse random access iterator
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circular_iterator A circular random access iterator 20.34.0
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circular_reverse_iterator A reverse circular random access iterator 20.34.0
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```
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## Constructors
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```cpp
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ETL_CONSTEXPR span()
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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 TIterator>
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ETL_CONSTEXPR span(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 span(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 span(element_type(&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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template <typename U, size_t N>
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ETL_CONSTEXPR span(etl::array<U, N>& a) ETL_NOEXCEPT
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```
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**Description**
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Construct from an ETL array.
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---
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```cpp
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template <typename U, size_t N>
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ETL_CONSTEXPR span(const etl::array<U, N>& a) ETL_NOEXCEPT
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```
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**Description**
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Construct from a const ETL array.
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---
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```cpp
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template <typename U, size_t N>
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ETL_CONSTEXPR span(std::array<U, N>& a) ETL_NOEXCEPT
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```
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**Description**
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Enabled if `ETL_USING_CPP11` and `ETL_USING_STL` are `true`.
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Construct from an STL array.
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---
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```cpp
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template <typename U, size_t N>
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ETL_CONSTEXPR span(const std::array<U, N>& a) ETL_NOEXCEPT
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```
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**Description**
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Enabled if `ETL_USING_CPP11` and `ETL_USING_STL` are `true`.
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Construct from a const STL array.
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---
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```cpp
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ETL_CONSTEXPR span(const span& other) ETL_NOEXCEPT
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```
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**Description**
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Copy constructor.
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---
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```cpp
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template <typename U, size_t N>
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ETL_CONSTEXPR span(const etl::span<U, N>& other) ETL_NOEXCEPT
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```
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## Access
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```cpp
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ETL_CONSTEXPR reference operator[](size_t i) const
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```
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**Description**
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Returns a reference to the indexed element.
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Index out of range results in undefined behaviour.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR reference front() const ETL_NOEXCEPT
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```
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**Description**
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Returns a reference to the first element.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR reference back() const ETL_NOEXCEPT
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```
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**Description**
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Returns a reference to the last element.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR pointer data() const ETL_NOEXCEPT
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```
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**Description**
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Returns a pointer to the first element.
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---
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```cpp
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ETL_CONSTEXPR14 span& operator =(const span& other) ETL_NOEXCEPT
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```
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**Description**
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Assign from a other span
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---
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```cpp
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template <size_t COUNT>
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ETL_NODISCARD ETL_CONSTEXPR etl::span<element_type, COUNT> first() const
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```
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**Description**
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Returns a span consisting of the first `COUNT` elements of the current span
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---
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```cpp
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template <size_t COUNT>
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ETL_NODISCARD ETL_CONSTEXPR etl::span<element_type, COUNT> last() const
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```
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**Description**
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Returns a span consisting of the last `COUNT` elements of the current span
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---
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```cpp
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template <size_t OFFSET, size_t COUNT = etl::dynamic_extent>
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ETL_NODISCARD ETL_CONSTEXPR etl::span<element_type, E> subspan() const
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```
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**Description**
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Returns a subspan consisting of the range starting at `OFFSET` for `COUNT` elements of the current span
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## Iterators
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR iterator begin() const ETL_NOEXCEPT
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```
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**Description**
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Returns an iterator to the beginning of the span.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR circular_iterator begin_circular() const ETL_NOEXCEPT
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```
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**Description**
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Returns a circular iterator to the beginning of the span.
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Since: `20.34.0`
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR iterator end() const ETL_NOEXCEPT
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```
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**Description**
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Returns an iterator to the end of the span.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR iterator rbegin() const ETL_NOEXCEPT
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```
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**Description**
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Returns a reverse iterator to the beginning of the span.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR reverse_circular_iterator rbegin_circular() const ETL_NOEXCEPT
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```
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**Description**
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Returns a reverse circular iterator to the beginning of the span.
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Since: `20.34.0`
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR iterator rend() const ETL_NOEXCEPT
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```
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**Description**
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Returns a reverse iterator to the end of the span.
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## Capacity
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR bool empty() const ETL_NOEXCEPT
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```
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**Description**
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Returns `true` if the size of the span is zero, otherwise `false`.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR size_t size() const ETL_NOEXCEPT
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```
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**Description**
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Returns the size of the span.
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---
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```cpp
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ETL_NODISCARD ETL_CONSTEXPR size_t size_bytes() const ETL_NOEXCEPT
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```
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**Description**
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Returns the size of the span in bytes.
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## Non-member functions
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```cpp
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template <typename T1, size_t N1, typename T2, size_t N2>
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ETL_NODISCARD
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ETL_CONSTEXPR
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bool operator ==(const etl::span<T1, N1>& lhs, const etl::span<T2, N2>& rhs) ETL_NOEXCEPT
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```
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**Description**
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Compare two spans for equality.
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Returns true if they both point to the same range of data.
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Since: `20.35.12`
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---
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```cpp
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template <typename T1, size_t N1, typename T2, size_t N2>
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ETL_NODISCARD
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ETL_CONSTEXPR
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bool operator !=(const etl::span<T1, N1>& lhs, const etl::span<T2, N2>& rhs) ETL_NOEXCEPT
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```
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**Description**
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Compare two spans for inequality.
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Returns true if they don't both point to the same range of data.
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Since: `20.35.12`
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---
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```cpp
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template <typename T1, size_t N1, typename T2, size_t N2>
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bool equal(const etl::span<T1, N1>& lhs, const etl::span<T2, N2>& rhs)
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```
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**Description**
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Equality function.
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Performs a comparision of the range values.
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Returns `true` if one of the following are `true`
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1. Both spans are empty.
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2. They both point to the same range of data.
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3. The values in the two ranges are equal.
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Since: `20.35.12`
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## Hash
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There is a specialisation of etl::hash for etl::span
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### Example
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**Iterating through a span and subspan.**
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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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using View = etl::span<int>;
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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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auto subview = view.subspan<2, 3>();
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Print(subview); // Prints "5 6 7"
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size_t hashvalue = etl::hash<View>()(view);
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```
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**Looping a span.**
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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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using View = etl::span<int>;
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View view(data.begin(), data.end());
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View::circular_iterator itr = view.begin_circular();
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// Loop through the data for 1000 iterations.
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for (int i; i < 1000; ++i)
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{
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Print(*itr++);
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}
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```
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