Why is a type alias not allowed to be a friend class name in C++?

While it's true that type aliases can be used as friend class names in C++, there is a subtle difference in syntax that can lead to confusion.

The correct syntax for befriending an alias C is friend C; instead of friend class C;.

When you write friend class C; you're actually making a global class named C a friend of B. To make the alias a friend, you just need to remove the class keyword.

class B { public: friend C; // Alias C is a friend of B };

This will allow the alias C to access the private and protected members of class B.

It's important to note that type aliases are not actual types in C++, they are simply another name for an existing type. This means that when you befriend an alias, you're actually befriending the underlying type.

typedef int MyInt; friend MyInt; // This is the same as friend int;

In this example, befriending the alias MyInt is the same as befriending the built-in type int.

I hope this clarifies the issue. If you have any further questions, feel free to ask.