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94 lines
2.2 KiB
Markdown
94 lines
2.2 KiB
Markdown
---
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title: "parameter_pack"
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---
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{{< callout type="info">}}
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Header: `parameter_pack.h`
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For C++11 or above
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{{< /callout >}}
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{{< callout type="warning">}}
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**This class is deprecated.**
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Use `etl::type_list` as a replacement.
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{{< /callout >}}
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Compile time mapping of index to type and type to index for a template parameter pack.
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## parameter_pack
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```cpp
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template <typename... TTypes>
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class parameter_pack
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```
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## Constants
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```cpp
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static constexpr size_t size = sizeof...(TTypes);
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```
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## Template alias
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```cpp
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template <size_t Index, typename... TTypes>
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using parameter_pack_t
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= typename etl::parameter_pack<TTypes...>::template type_from_index_t<Index>;
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```
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Type from index and type list.
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**For C++17 or above**
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```cpp
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template <typename T, typename... TTypes>
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inline constexpr size_t parameter_pack_v
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= etl::parameter_pack<TTypes...>::template index_of_type<T>::value;
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```
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Index from type and type list.
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**The class contains two nested templates.**
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## index_of_type
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```cpp
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template <typename T>
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class index_of_type
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```
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**For C++17 or above**
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```cpp
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template <typename T>
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static constexpr size_t index_of_type_v = index_of_type<T>::value;
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```
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## type_from_index
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```cpp
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template <size_t Index>
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class type_from_index
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```
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---
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```cpp
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template <size_t Index>
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using type_from_index_t = typename type_from_index<Index>::type;
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```
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## Examples
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```cpp
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using Pack = etl::parameter_pack<char, short, int>;
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constexpr size_t size = Pack::size; // size == 3
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size_t indexChar = Pack::index_of_type_v<char>; // indexChar == 0
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size_t indexShort = Pack::index_of_type_v<short>; // indexShort == 1
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size_t indexInt = Pack::index_of_type_v<int>; // indexInt == 2
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size_t indexLong = Pack::index_of_type_v<long>; // Static assert
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// "T is not in parameter pack"
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using type0 = typename Pack::type_from_index_t<0>; // type0 = char
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using type1 = typename Pack::type_from_index_t<1>; // type1 = short
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using type2 = typename Pack::type_from_index_t<2>; // type2 = int
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using type3 = typename Pack::type_from_index_t<3>; // Static assert
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// "Index out of bounds of parameter pack"
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```
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