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std::decay

From cppreference.com
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decay
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Defined in header <type_traits>
template< class T >
struct decay;
(since C++11)

Applies lvalue-to-rvalue, array-to-pointer, and function-to-pointer implicit conversions to the type T, removes cv-qualifiers, and defines the resulting type as the member typedef type. This is the type conversion applied to all function arguments when passed by value.

Contents

[edit] Member types

Name Definition
type the result of applying the decay type conversions to T

[edit] Helper types

template< class T >
using decay_t = typename decay<T>::type;
(since C++14)

[edit] Possible implementation

template< class T >
struct decay {
    typedef typename std::remove_reference<T>::type U;
    typedef typename std::conditional< 
        std::is_array<U>::value,
        typename std::remove_extent<U>::type*,
        typename std::conditional< 
            std::is_function<U>::value,
            typename std::add_pointer<U>::type,
            typename std::remove_cv<U>::type
        >::type
    >::type type;
};

[edit] Example

#include <iostream>
#include <type_traits>
 
template <typename T, typename U>
struct decay_equiv : 
    std::is_same<typename std::decay<T>::type, U>::type 
{};
 
int main()
{
    std::cout << std::boolalpha
              << decay_equiv<int, int>::value << '\n'
              << decay_equiv<int&, int>::value << '\n'
              << decay_equiv<int&&, int>::value << '\n'
              << decay_equiv<const int&, int>::value << '\n'
              << decay_equiv<int[2], int*>::value << '\n'
              << decay_equiv<int(int), int(*)(int)>::value << '\n';
}

Output:

true
true
true
true
true
true

[edit] See also

implicit conversion array-to-pointer, function-to-pointer, rvalue-to-lvalue conversions