std::decay
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | 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:
-  If Tnames the type "array ofU" or "reference to array ofU", the member typedeftypeis U*.
-  Otherwise, if Tis a function typeFor a reference thereto, the member typedeftypeis std::add_pointer<F>::type.
-  Otherwise, the member typedef typeis std::remove_cv<std::remove_reference<T>::type>::type.
These conversions model 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 { 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; }; | 
[edit] Example
Run this code
#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, lvalue-to-rvalue conversions | 


