How do you mark a struct template as friend?

问题

I have code like this:

template <typename T, typename U> struct MyStruct {
    T aType;
    U anotherType;
};

class IWantToBeFriendsWithMyStruct
{
    friend struct MyStruct; //what is the correct syntax here ?
};

What is the correct syntax to give friendship to the template ?

回答1:

class IWantToBeFriendsWithMyStruct
{
    template <typename T, typename U>
    friend struct MyStruct;
};

Works in VS2008, and allows MyStruct to access the class.

回答2:

According to this site, the correct syntax would be

class IWantToBeFriendsWithMyStruct
{
    template <typename T, typename U> friend struct MyStruct; 
}

来源：https://stackoverflow.com/questions/206045/how-do-you-mark-a-struct-template-as-friend