Re: mixing bound and unbound friends
On 23 ec, 13:32, Christof Warlich <cwarl...@gmx.de> wrote:
Hi,
I need to make a templated class A a friend of class B.
My problem: I think I know how to do this for both
1) _one_ specific template instantiation of class A, e.g.:
template<typename Type, unsigned int x> class A {
public:
void useSomeFunctionalityOfB(void);};
class B {
friend class A<float, 7>;
};
2) _any_ instantiation of class A, e.g.:
template<typename Type, unsigned int x> class A {
public:
void useSomeFunctionalityOfB(void);};
class B {
template<typename Type, unsigned int x> friend class A;
};
But I do _not_ know how to mix the two extremes, e.g.
how to make class A a friend of class B only for Type float,
but for any unsigned int x.
Is it possible to express this at all, and if so, how?
Thanks for any help,
Christof
Hi Christof.
You can define intermediate access class which is templated only with
one parameter:
#include <iostream>
template<typename T> struct AccessB;
class B {
friend struct AccessB<float>; // Make only AccessB<float> friend
private:
static void MethodOfB() { std::cout << "B::MethodOfB()\n"; }
};
template<typename T> struct AccessB {
static void useSomeFunctionalityOfB()
{
B::MethodOfB();
}
};
template<typename Type, unsigned int x> class A {
public:
A() { }
void useSomeFunctionalityOfB()
{
// This will compile only when Type is float
AccessB<Type>::useSomeFunctionalityOfB();
}
};
int main()
{
// This is OK
A<float, 10> af10;
af10.useSomeFunctionalityOfB();
// The following will not compile
// A<double, 10> ad10;
// ad10.useSomeFunctionalityOfB();
}
If you uncomment last 2 lines in main(), you will get compile error,
because you will be trying to access private member of B. It is a bit
obscure, but maybe it could help you.