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532 lines
8.6 KiB
Markdown
532 lines
8.6 KiB
Markdown
---
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title: "Utility"
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---
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{{< callout type="info">}}
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Header: `utility.h`
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{{< /callout >}}
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Useful utility functions and classes.
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## pair
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```cpp
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template <typename T1, typename T2>
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struct pair
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```
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**Description**
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A clone of std::pair
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**C++03**
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```cpp
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template <typename T1, typename T2>
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pair<T1, T2> make_pair(T1 a, T2 b)
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```
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**C++11 and above**
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```cpp
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template <typename T1, typename T2>
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pair<T1, T2> make_pair(T1&& a, T2&& b)
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```
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**Description**
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Returns a pair.
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---
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```cpp
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template <size_t Index, typename T1, typename T2>
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struct tuple_element<Index, ETL_OR_STD::pair<T1, T2>>
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```
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**Description**
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Specialisation for pair.
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Gets the type in the pair at `Index`.
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Static asserts if `Index` is not `0` or `1`.
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Since: `20.40.1`
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---
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```cpp
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template <typename T1, typename T2>
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struct tuple_size<ETL_OR_STD::pair<T1, T2>>
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```
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**Description**
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Specialisation for pair.
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Gets the size of the pair, which is always `2`.
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Since:`20.40.1`
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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 T1, typename T2>
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pair(T1, T2) ->pair<T1, T2>;
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```
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## exchange
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```cpp
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template <typename T, typename U = T>
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T exchange(T& object, const U& new_value)
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```
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**Description**
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Copies the new value to object and returns the old value.
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Note: This is not an atomic operation.
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## add_const
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```cpp
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template <typename T>
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typename etl::add_const<T>::type& as_const(T& t)
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```
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**Description**
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Returns a value of type `T` as a `const T`.
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## coordinate_2d
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```cpp
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template <typename T>
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struct coordinate_2d
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```
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**Member types**
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`T x;`
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`T y;`
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## in_place disambiguation tags.
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```cpp
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struct in_place_t
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```
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```cpp
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inline constexpr in_place_t in_place{}; // C++17
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```
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---
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```cpp
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template <typename T> struct in_place_type_t
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```
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```cpp
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template <typename T>
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inline constexpr in_place_type_t<T> in_place_type{}; // C++17
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```
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---
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```cpp
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template <size_t I> struct in_place_index_t
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```
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```cpp
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template <size_t I>
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inline constexpr in_place_index_t<I> in_place_index{}; // C++17
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```
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## declval
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```cpp
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template <typename T>
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typename etl::add_rvalue_reference<T>::type declval() ETL_NOEXCEPT;
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```
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C++11
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## functor
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For C++11 and above.
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Since: `20.27.0`
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```cpp
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template <typename TReturn, typename... TParams>
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class functor
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```
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**Description**
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Wraps a free/global function in a functor.
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---
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```cpp
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constexpr functor(TReturn(*ptr_)(TParams...))
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```
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Constructs a functor from a function pointer.
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---
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```cpp
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constexpr TReturn operator()(TParams... args) const
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```
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**Description**
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Function operator.
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Calls the wrapped function with the forwarded parameters.
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### Example
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```cpp
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void int Function(int i)
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{
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return i;
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}
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// Note that the functor deduces the template parameters.
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constexpr etl::functor f(Function);
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```
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---
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## member_function_wrapper
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For C++11 and above.
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Since: `20.27.0`
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```cpp
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template <typename TReturn, typename... TParams>
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class member_function_wrapper<TReturn(TParams...)>
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```
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**Description**
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Wraps a member function in a static member function.
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---
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```cpp
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template <typename T, T& Instance, TReturn(T::* Method)(TParams...)>
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static constexpr TReturn function(TParams... params)
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```
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**Description**
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The static function that calls the member function.
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### Example
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```cpp
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class MyClass
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{
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public:
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int MemberFunction(int i)
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{
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return 2 * i;
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}
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};
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MyClass test;
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constexpr int(*pf)(int)
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= &etl::member_function_wrapper<int(int)>::function<MyClass, test, &MyClass::MemberFunction>;
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// Call
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int result = pf(1);
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```
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## functor_wrapper
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For C++11 and above.
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Since: `20.27.0`
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```cpp
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template <typename TReturn, typename... TParams>
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class functor_wrapper<TReturn(TParams...)>
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```
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**Description**
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Wraps a functor in a static member function.
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---
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```cpp
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template <typename TFunctor, TFunctor& Instance>
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static constexpr TReturn function(TParams... params)
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```
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**Description**
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The static function that calls the member function.
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### Example
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```cpp
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class MyClass
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{
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public:
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int operator()(int i)
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{
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return 2 * i;
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}
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};
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MyClass test;
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constexpr int(*pf)(int) = &etl::functor_wrapper<int(int)>::function<MyClass, test>;
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// Call
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int result = pf(1);
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```
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## functor_as_static
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For C++17 and above.
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20.40.0
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Wraps a functor with a static free function at compile time.
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Creates a static member `call` that calls the specified functor.
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```cpp
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template <auto& Instance>
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struct functor_as_static
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```
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---
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```cpp
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template <typename... TArgs>
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static constexpr auto call(TArgs&&... args)
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```
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**Description**
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Member static function that calls the functor
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### Example
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```cpp
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struct Test
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{
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int operator()(int i)
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{
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return 2 * i;
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}
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};
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Test test;
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using fas_t = etl::functor_as_static<test>;
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fas_t::call(1));
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```
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## member_function_as_static
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For C++17 and above.
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Since: `20.40.0`
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Wraps a member function with a static free function at compile time.
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Creates a static member function that calls the specified member function.
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```cpp
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template <auto Method, auto& Instance>
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struct member_function_as_static
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```
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---
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```cpp
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template <typename... TArgs>
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static constexpr auto call(TArgs&&... args)
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```
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**Description**
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Member static function that calls the member function.
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### Example
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```cpp
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struct Test
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{
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int Function()(int i)
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{
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return 2 * i;
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}
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};
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Test test;
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using mfas_t = etl::functor_as_static<&Test::Function, test>;
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mfas_t::call(1));
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```
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## member_function_as_functor
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For C++17 and above.
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Since: `20.40.0`
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Wraps a member function with a functor at compile time.
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Creates a functor that calls the specified member function.
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```cpp
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template <auto Method, auto& Instance>
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class member_function_as_functor
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```
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---
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```cpp
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template <typename... TArgs>
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constexpr auto operator()(TArgs&&... args) const
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```
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**Description**
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Calls the functor.
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### Example
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```cpp
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struct Test
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{
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int Function()(int i)
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{
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return 2 * i;
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}
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};
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constexpr etl::member_function_as_functor<&Test::Function, test> mfaf;
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mfaf(1);
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```
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## function_as_functor
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For C++17 and above.
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Since: `20.40.0`
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Wraps a function with a functor at compile time.
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Creates a functor that calls the specified free function.
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```cpp
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template <auto Function>
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class function_as_functor
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```
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---
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```cpp
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constexpr auto operator()(TArgs&&... args) const
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```
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**Description**
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Calls the functor.
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### Example
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```cpp
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int Function()(int i)
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{
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return 2 * i;
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}
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constexpr etl::function_as_functor<Function> faf;
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faf(1);
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```
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## function_ptr_as_functor
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For C++11 and above.
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Since: `20.40.0`
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Wraps a function pointer with a functor at run time.
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Creates a functor that calls the specified free function.
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```cpp
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template <typename TReturn, typename... TArgs>
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class function_ptr_as_functor
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```
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---
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```cpp
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constexpr function_ptr_as_functor(TReturn(*ptr_)(TArgs...))
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```
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**Description**
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Construct from a function pointer.
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---
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```cpp
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constexpr TReturn operator()(TArgs... args) const
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```
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**Description**
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Function operator.
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### Example
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```cpp
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int Function()(int i)
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{
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return 2 * i;
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}
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using function_type = decltype(Function);
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constexpr function_type* fptr = Function;
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constexpr etl::function_ptr_as_functor<function_type> fpaf(fptr)
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```
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## integer_sequence
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Since: `20.14.0`
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```cpp
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template <typename T, T... Integers>
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class integer_sequence
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```
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## index_sequence
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Since: `20.14.0`
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```cpp
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template <size_t... Indices>
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using index_sequence = etl::integer_sequence<size_t, Indices...>;
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```
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```cpp
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template <size_t N>
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make_index_sequence
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```
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## select1st & select2nd
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`select1st`
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A functor object that takes a single argument, a pair, and returns the `pair::first element`.
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---
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`select2nd`
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A functor object that takes a single argument, a pair, and returns the `pair::second element`.
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## size_of_type
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Since: `20.36.0`
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```cpp
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template <typename T>
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ETL_CONSTEXPR size_t size_of_type()
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```
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**Description**
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Returns the size of the type defined in `T`.
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---
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```cpp
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template <typename T>
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ETL_CONSTEXPR size_t size_of_type(const T&)
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```
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**Description**
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Returns the size of the type defined in `T`.
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---
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```cpp
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ETL_SIZE_OF_OBJECT_TYPE(Object, Type)
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```
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**Description**
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Returns the size of `Type` defined in the declared type of `Object`.
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C++11 and above.
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Since: `20.36.0`
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```cpp
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ETL_SIZE_OF_CLASS_TYPE(Class, Type)
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```
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**Description**
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Returns the size of `Type` defined in `Class`.
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Since: `20.36.0`
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---
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## nontype_t
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Since `20.43.0`
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Wraps a non-type template parameter as a type.
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Defines a value associated with the template type.
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If `ETL_FORCE_CPP11_NONTYPE` is defined then the C++14 and below variant is used.
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**C++14 and below**
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```cpp
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template <typename T, T Value>
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struct nontype_t;
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```
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```cpp
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using FortyTwo = etl::nontype_t<int, 42>;
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```
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**C++17 and above**
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```cpp
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template <auto Value>
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struct nontype_t;
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```
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```cpp
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using FortyTwo = etl::nontype_t<42>
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```
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