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Difference between revisions of "cpp/container/array/tuple element"

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< cpp‎ | container‎ | array
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{{cpp/title|tuple_element{{small|<std::array>}}}}
 
{{cpp/title|tuple_element{{small|<std::array>}}}}
 
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{{dcl begin}}
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{{ddcl list header | array}}
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template< std::size_t I, class T, std::size_t N >
 
template< std::size_t I, class T, std::size_t N >
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struct tuple_element<I, array<T, N> >;
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struct tuple_element< I, std::array<T, N> >;
 
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{{dcl end}}
  
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Provides compile-type indexed access to the type of the elements of the array using tuple-like interface
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Provides compile-time indexed access to the type of the elements of the array using tuple-like interface.
  
 
===Member types===
 
===Member types===
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{{dcl list hitem | Member type | Definition}}
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{{dsc hitem|Member type|Definition}}
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{{dcl list item | type | the type of elements of the array}}
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{{dsc|type|the type of elements of the array}}
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{{dsc end}}
  
 
===Possible implementation===
 
===Possible implementation===
 
{{eq fun
 
{{eq fun
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| 1=
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template<std::size_t I, class T>
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struct tuple_element;
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template<std::size_t I, class T, std::size_t N>
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struct tuple_element<I, std::array<T,N>>
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{
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    using type = T;
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};
 
}}
 
}}
  
 
===Example===
 
===Example===
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{{example |
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{{example
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|code=
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#include <array>
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#include <tuple>
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#include <type_traits>
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int main()
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{
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    // define array and get the type of the element at position 0
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    std::array<int, 10> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
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    using T = std::tuple_element<0, decltype(data)>::type; // int
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    static_assert(std::is_same_v<T, int>);
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    const auto const_data = data;
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    using CT = std::tuple_element<0, decltype(const_data)>::type; // const int
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 +
    // the result of tuple_element depends on the cv-qualification of the tuple-like type
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    static_assert(!std::is_same_v<T, CT>);
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    static_assert(std::is_same_v<CT, const int>);
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}
 
}}
 
}}
  
 
===See also===
 
===See also===
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{{dcl list template | cpp/utility/tuple/dcl list tuple_element}}
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{{dsc inc|cpp/language/dsc structured binding}}
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{{dcl list template | cpp/utility/pair/dcl list tuple_element}}
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{{dsc inc|cpp/utility/tuple/dsc tuple_element}}
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{{dsc inc|cpp/utility/pair/dsc tuple_element}}
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{{dsc end}}
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 13:47, 6 December 2023

 
C++
 
Containers library
 
std::array
 
Defined in header <array>
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[edit]
(C++11)
 obtains the type of the specified element
(class template specialization) [edit]
(C++11)
 obtains the type of the elements of pair
(class template specialization) [edit]
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