'function' : pure specifier not allowed on friend functions
The specified friend function was specified as pure virtual.
The following is an example of this error:
class A
{
public:
friend void func1() = 0; // error, func1 is friend
void virtual func2() = 0; // OK, pure virtual
friend void func3(); // OK, friend not virtual nor
}; // pure
void func1() {};
void func3() {};