模板化代理设计模式

问题描述

我有一个简单且可复制的代码，如下所示：

I have a simple and reproducible code, which looks like so:

template <typename T>
class Proxy {
private:
    Wrap<T> &self; // If I comment this, it will work
public:
    Proxy() {}
};

template <typename T>
class Wrap {
    T *p;
public:
    Proxy<T> foo() {
        return Proxy<T>();
    }
};

int main()
{
    return 0;
}

我得到的错误是：

如果我评论包装< T> & self ，那么它将起作用，但这不是我所需要的。我需要 Wrap< T> 成为 Proxy 类的成员。我该如何实现？

If I comment Wrap<T> &self, then it will work, but this is not what I need. I need Wrap<T> to be a member of Proxy class. How can I achieve this?

推荐答案

您可以添加（在 Proxy ，否则编译器无法知道它是类模板的名称。值得注意的是，引用数据成员不需要类型为，因此在这里前向声明就足够了。

You could add forward declaration of Wrap before the class definition of Proxy, otherwise the compiler can't know that it's the name of a class template. It's worth noting that reference data member doesn't require the type to be complete type, so forward declaration is enough here.

// forward declaration
template <typename T>
class Wrap;

template <typename T>
class Proxy {
private:
    Wrap<T> &self;
public:
    Proxy() {}
};

顺便说一句，下面的问题是引用数据成员 self 未初始化。

BTW the following issue would be that the reference data member self is not initialized.

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