如何传递std :: unique_ptr？ [英] How to pass std::unique_ptr around?

问题描述

我第一次尝试使用C ++ 11 unique_ptr ;我正在替换我的一个项目中的多态原始指针，该项目属于一个类，但是经常通过。

I am having my first attempt at using C++11 unique_ptr; I am replacing a polymorphic raw pointer inside a project of mine, which is owned by one class, but passed around quite frequently.

我曾经有以下功能：

I used to have functions like:

bool func(BaseClass* ptr, int other_arg) {
  bool val;
  // plain ordinary function that does something...
  return val;
}

但是我很快意识到我将无法切换到： / p>

But I soon realized that I wouldn't be able to switch to:

bool func(std::unique_ptr<BaseClass> ptr, int other_arg);

因为调用者必须处理该函数的指针所有权，所以我不想。那么，解决我的问题的最佳方法是什么？

Because the caller would have to handle the pointer ownership to the function, what I don't want to. So, what is the best solution to my problem?

我虽然将指针作为参考传递，例如：

I though of passing the pointer as reference, like this:

bool func(const std::unique_ptr<BaseClass>& ptr, int other_arg);

但是我这样做非常不自在，首先是因为通过本来就是已经输入的东西似乎不是本能。 _ptr 作为参考，这将是参考的参考。其次，因为功能签名变得更大。第三，因为在生成的代码中，需要两个连续的指针间接访问才能到达我的变量。

But I feel very uncomfortable in doing so, firstly because it seems non instinctive to pass something already typed as _ptr as reference, what would be a reference of a reference. Secondly because the function signature gets even bigger. Thirdly, because in the generated code, it would be necessary two consecutive pointer indirections to reach my variable.

推荐答案

函数使用pointee，传递对它的引用。没有理由将函数仅与某种智能指针配合使用：

If you want the function to use the pointee, pass a reference to it. There's no reason to tie the function to work only with some kind of smart pointer:

bool func(BaseClass& base, int other_arg);

在呼叫站点使用 operator * ：

func(*some_unique_ptr, 42);

或者，如果允许 base 自变量为null，请保持签名不变，并使用 get（）成员函数：

Alternatively, if the base argument is allowed to be null, keep the signature as is, and use the get() member function:

bool func(BaseClass* base, int other_arg);
func(some_unique_ptr.get(), 42);

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