使用decltype

问题描述

T *t; //T is an implementation detail
t = new T; //want to avoid naming T to allow for flexibility
t = new decltype(*t); //error: cannot use 'new' to allocate a reference
t = new std::remove_reference<decltype(*t)>::type(); //clunky

回答为什么 decltype（* t）返回 T& ，而不是 T 。

This answers why decltype(*t) returns T & and not T.

我可以把我的最后一行放入一个宏，但似乎不太理想。
有没有比我迄今为止更好的解决方案？这是否属于？

I can put my last line into a macro, but that seems suboptimal.Is there a better solution than what I have so far? Does this belong on Code Review?

推荐答案

如果他们在同一行，您可以使用 auto 只输入 T 一次：

If they're on the same line, you can use auto to only name T once:

auto t = new T;

否则，您可以创建一个小函数模板：

Otherwise, you could create a small function template:

template <class T>
void do_new(T * &p) {
  p = new T;
}


// Usage:
int main()
{
  T *t;
  do_new(t);
}

正如@MadScienceDreams指出的，您可以将其扩展为允许非默认构造函数：

As @MadScienceDreams pointed out, you can extend this to allow non-default constructors:

template <class T, class... Arg>
void do_new(T * &p, Arg &&... arg) {
  p = new T(std::forward<Arg>(arg)...);
}


// Usage:
int main()
{
  T *t;
  do_new(t);
  std::string *s;
  do_new(s, "Abc");
}

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