Templated Proxy design pattern - c++

Question

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;
}
The error I get is:
'Wrap' does not name a type
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?

Answer 1

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() {}
};
BTW the following issue would be that the reference data member self is not initialized.
LIVE of Clang
error: constructor for 'Proxy' must explicitly initialize the reference member 'self'

Answer 2

You need to add a forward declaration:
template<class T> class Wrap;
template <typename T>
class Proxy {
private:
Wrap<T> &self;
public:
Proxy() {}
};
template <typename T>
class Wrap {
T *p;
public:
Proxy<T> foo() {
return Proxy<T>();
}
};
int main()
{
return 0;
}
The code is just copied from the OP's question. But you still need to pay a attention to member Wrap<T> &self. As a reference, it should be initialized in constructor.