Difference between revisions of "cpp/container/array/tuple element"
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{{cpp/container/array/navbar}} | {{cpp/container/array/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | array}} | + | {{dcl header|array}} |
| − | {{dcl | since=c++11 | 1= | + | {{dcl|since=c++11|1= |
template< std::size_t I, class T, std::size_t N > | template< std::size_t I, class T, std::size_t N > | ||
| − | struct tuple_element<I, array<T, N> >; | + | struct tuple_element< I, std::array<T, N> >; |
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| − | Provides compile-time indexed access to the type of the elements of the array using tuple-like interface | + | Provides compile-time indexed access to the type of the elements of the array using tuple-like interface. |
===Member types=== | ===Member types=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc hitem | Member type | Definition}} | + | {{dsc hitem|Member type|Definition}} |
| − | {{dsc | type | the type of elements of the array}} | + | {{dsc|type|the type of elements of the array}} |
{{dsc end}} | {{dsc end}} | ||
===Possible implementation=== | ===Possible implementation=== | ||
{{eq fun | {{eq fun | ||
| − | + | |1= | |
template<std::size_t I, class T> | template<std::size_t I, class T> | ||
| − | + | struct tuple_element; | |
template<std::size_t I, class T, std::size_t N> | template<std::size_t I, class T, std::size_t N> | ||
| − | + | struct tuple_element<I, std::array<T,N>> | |
| − | + | { | |
| − | + | using type = T; | |
| − | + | }; | |
}} | }} | ||
===Example=== | ===Example=== | ||
| − | {{example | + | {{example |
| − | + | |code= | |
#include <array> | #include <array> | ||
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#include <tuple> | #include <tuple> | ||
#include <type_traits> | #include <type_traits> | ||
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int main() | int main() | ||
{ | { | ||
| − | + | // define array and get the type of the element at position 0 | |
| − | + | std::array<int, 10> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; | |
| − | + | using T = std::tuple_element<0, decltype(data)>::type; // int | |
| − | + | static_assert(std::is_same_v<T, int>); | |
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| − | + | const auto const_data = data; | |
| − | + | using CT = std::tuple_element<0, decltype(const_data)>::type; // const int | |
| − | + | // the result of tuple_element depends on the cv-qualification of the tuple-like type | |
| − | + | static_assert(!std::is_same_v<T, CT>); | |
| + | static_assert(std::is_same_v<CT, const int>); | ||
} | } | ||
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}} | }} | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/utility/tuple/dsc tuple_element}} | + | {{dsc inc|cpp/language/dsc structured binding}} |
| − | {{dsc inc | cpp/utility/pair/dsc tuple_element}} | + | {{dsc inc|cpp/utility/tuple/dsc tuple_element}} |
| + | {{dsc inc|cpp/utility/pair/dsc tuple_element}} | ||
{{dsc end}} | {{dsc end}} | ||
| − | + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | |
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Latest revision as of 13:47, 6 December 2023
| Defined in header <array>
|
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| template< std::size_t I, class T, std::size_t N > struct tuple_element< I, std::array<T, N> >; |
(since C++11) | |
Provides compile-time indexed access to the type of the elements of the array using tuple-like interface.
Contents |
[edit] Member types
| Member type | Definition |
| type | the type of elements of the array |
[edit] Possible implementation
template<std::size_t I, class T> struct tuple_element; template<std::size_t I, class T, std::size_t N> struct tuple_element<I, std::array<T,N>> { using type = T; }; |
[edit] Example
Run this code
#include <array> #include <tuple> #include <type_traits> int main() { // define array and get the type of the element at position 0 std::array<int, 10> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; using T = std::tuple_element<0, decltype(data)>::type; // int static_assert(std::is_same_v<T, int>); const auto const_data = data; using CT = std::tuple_element<0, decltype(const_data)>::type; // const int // the result of tuple_element depends on the cv-qualification of the tuple-like type static_assert(!std::is_same_v<T, CT>); static_assert(std::is_same_v<CT, const int>); }
[edit] See also
| Structured binding (C++17) | binds the specified names to sub-objects or tuple elements of the initializer |
| obtains the type of the specified element (class template specialization) | |
obtains the type of the elements of pair (class template specialization) |
