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std::decay

性病：衰变

Defined in header ​​
template< class T > struct decay;​(since C++11)

将lvalue到rvalue、数组到指针以及函数到指针的隐式转换应用于类型。T，移除cv-限定符，并将结果类型定义为type.正式：

  • 如果T命名类型“数组U“或”引用U“，成员类型ftype是U*...

  • 否则，如果T是函数类型F或对该成员的引用，type是std::add_pointer<F>::type...

  • 否则，则为type是std::remove_cv<std::remove_reference<T>::type>::type...

这些转换建立了类型转换的模型，当通过值传递时，类型转换应用于所有函数参数。

成员类型

NameDefinition
typethe result of applying the decay type conversions to T

帮助者类型

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

可能的实施

模板<class T>结构衰变{私有：tyduif类型名称STD：：Remove[医]参照系<T>：：U类型；public：tyduif type Name std：：条件<std：：is[医]列阵<U>*值，类型名称STD：：Remove[医]程度<U>*类型%2A，类型名称std：：条件<std：：is[医]功能<U>*value，type name std：：：Add[医]指针<U>*输入，类型名称STD：：删除[医]CV<U>*类型>：类型>：类型；}；

*。

例

二次

#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';
}

二次

产出：

二次

true
true
true
true
true
true

二次

另见

implicit conversionarray-to-pointer, function-to-pointer, lvalue-to-rvalue conversions

 © cppreference.com

在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/type/衰减

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