C++

参考

<type_traits>

类模板
<type_traits>

std::decay

template <class T> struct decay;
Decay type
Obtains the decay type ofT.

转换后的类型别名为成员类型decay::type.

The decay type ofTis the same type that results from the standard conversions that happen when an lvalue expression is used as an rvalue, with its cv-qualifier stripped


This resembles the implicit conversions happening when an argument is passed by value to a function.

请注意，此类仅使用另一种类型作为模型来获取类型，但它不会在这些类型之间转换值或对象。

模板参数

T
一个类型。

成员类型

成员类型定义
类型如果已知Tis a reference type, the type referrered to byT.
否则，T.

示例

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// decay example
#include <iostream>
#include <type_traits>

typedef std::decay<int>::type A;           // int
typedef std::decay<int&>::type B;          // int
typedef std::decay<int&&>::type C;         // int
typedef std::decay<const int&>::type D;    // int
typedef std::decay<int[2]>::type E;        // int*
typedef std::decay<int(int)>::type F;      // int(*)(int)

typedef int X[3];

int main() {
  std::cout << std::boolalpha;
  std::cout << "typedefs of int:" << std::endl;
  std::cout << "A: " << std::is_same<int,A>::value << std::endl;
  std::cout << "B: " << std::is_same<int,B>::value << std::endl;
  std::cout << "C: " << std::is_same<int,C>::value << std::endl;
  std::cout << "D: " << std::is_same<int,D>::value << std::endl;
  std::cout << "E: " << std::is_same<int,E>::value << std::endl;
  std::cout << "F: " << std::is_same<int,F>::value << std::endl;

  return 0;
}

输出
typedefs of int:
A: true
B: true
C: true
D: true
E: false
F: false


另见

underlying_type
Underlying type of enum (class template)
remove_reference
移除引用 （类模板）
remove_cv
移除 cv 限定 （类模板）