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
. Formally:
T
names the type "array of U
" or "reference to array of U
", the member typedef type
is U*
. T
is a function type F
or a reference thereto, the member typedef type
is std::add_pointer<F>::type
. type
is std::remove_cv<std::remove_reference<T>::type>::type
. These conversions model the type conversion applied to all function arguments when passed by value.
Name | Definition |
---|---|
type | the result of applying the decay type conversions to T |
template< class T > using decay_t = typename decay<T>::type; | (since C++14) |
template< class T > struct decay { private: typedef typename std::remove_reference<T>::type U; public: 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; }; |
#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
(C++20) | combines std::remove_cv and std::remove_reference (class template) |
implicit conversion | array-to-pointer, function-to-pointer, lvalue-to-rvalue conversions |
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