Let’s setup some constraints for refactoring first: The ClassAAccessor’s publicly visible interface should change in no way The ClassA internal operations should not be visible/accessible from the public The overall performance and footprint of the original design should not be hurt Step 1: Introduce an abstract interface For a first shot, I factored out the … Read more
class A{ public: friend void fun(A a){std::cout << “Im here” << std::endl;} friend void fun2(){ std::cout << “Im here2″ << std::endl; } friend void fun3(); }; Although your definition of fun2 does define a “global” function rather than a member, and makes it a friend of A at the same time, you are still missing … Read more
Thanks to your other question it looks like this pattern is now known as the “passkey” pattern. In C++11, it gets even cleaner, because instead of calling b.protectedMethod(SomeKey()); you can just call: b.protectedMethod({});
template<typename> friend class foo this will however make all templates friends to each other. But I think this is what you want?
On a side note. Using friend is not about violating the encapsulation, but on the contrary it’s about enforcing it. Like accessors+mutators, operators overloading, public inheritance, downcasting, etc., it’s often misused, but it does not mean the keyword has no, or worse, a bad purpose. See Konrad Rudolph‘s message in the other thread, or if … Read more
When you declare a friend function with an unqualified id in a class it names a function in the nearest enclosing namespace scope. If that function hasn’t previously been declared then the friend declaration doesn’t make that function visible in that scope for normal lookup. It does make the declared function visible to argument-dependent lookup. … Read more
I like this idiom, and it has the potential to become much cleaner and more expressive. In standard C++03, I think the following way is the easiest to use and most generic. (Not too much of an improvement, though. Mostly saves on repeating yourself.) Because template parameters cannot be friends, we have to use a … Read more
Here is a small trick that I use in JAVA to replicate C++ friend mechanism. Lets say I have a class Romeo and another class Juliet. They are in different packages (family) for hatred reasons. Romeo wants to cuddle Juliet and Juliet wants to only let Romeo cuddle her. In C++, Juliet would declare Romeo … Read more
Firstly (IMO) don’t listen to people who say friend is not useful. It IS useful. In many situations you will have objects with data or functionality that are not intended to be publicly available. This is particularly true of large codebases with many authors who may only be superficially familiar with different areas. There ARE … Read more
This is one of those frequently asked questions that have different approaches that are similar but not really the same. The three approaches differ in who you are declaring to be a friend of your function –and then on how you implement it. The extrovert Declare all instantiations of the template as friends. This is … Read more