How to Refactor a "friend" Dependency Declaration

Background

One may encounter a scenario where removing a "friend" dependency between two classes is desired, particularly due to concerns about excessive interdependency, maintenance issues, and outdated UML standards.

Step 1: Introduce an Abstract Interface

Extract the methods exposed by the "friend" class and create a new abstract interface. Establish a dependency relationship from the "friend" class to the interface and a "call" dependency from the other class to the interface.

Step 2: Move Operations to the Interface

Move the operations that make up the "call" dependency from the dependent class to the abstract interface. Make the interface extend a protected constructor for inheritance purposes and hide the protected generalization association between the dependent class and the interface.

Step 3: Glue Implementation Together

In the final step, create a method in the "friend" class to pass a reference of the abstract interface to the dependent class. Call this method from the dependent class during initialization to establish the necessary connection.

Implementation

ClassA (provider):

class ClassA : protected InternalInterface {
    public:
        attachAccessor(ClassAAccessor &accessor) {
            accessor.setInternalInterfaceRef(*this);
        }
};

ClassAAccessor (friend):

class ClassAAccessor {
    public:
        ClassAAccessor(ClassA& classA) : internalInterfaceRef(0) {
            classA.attachAccessor(*this);
        }
    private:  
        InternalInterface* internalInterfaceRef;
};

Advantages

• Removes unnecessary dependency between classes
• Conforms to modern UML standards
• Enforces access control by hiding internal operations from the public

Limitations

• May increase code complexity
• Requires abstract interfaces, impacting performance and memory footprint
• UML representation of protected generalization relationship can be challenging