What's the name of this design pattern? Façade, adapter, bridge, proxy?

Question

In one of my projects, I'm using the following pattern at several places: I have a class A with a bunch of methods, and class B which gets constructed with a pointer to some instance of A, exporting only a subset of those methods for a user (which is not the owner of the A instance).

class A
{
public:
    void doStuff();
    void doOtherStuff();
    void doYetOtherStuff();
    B getB()
    {
        return B(this);
    }
};

class B
{
    friend class A;

public:
    void doStuff()
    {
        _a->doStuff();
    }

    void doOtherStuff()
    {
        _a->doOtherStuff();
    }

private:
    B(A* a) : _a(a) {}
    A* _a;
};

An instance of A could be created by my library, for example, and a created instance of B (associated with an A) could be passed to a plugin, which will still have access to the A instance, albeit in a limited way.

I'm just confused regarding the design pattern name of B: is it a façade, a bridge, an adapter or a proxy? Or something else?

Answer 1

In this case, I would advise checking Huston Design Patterns. At the end of each pattern it cites the GoF and gives the differences between the current pattern and related patterns.

For example, on Proxy we can read:

Adapter provides a different interface to its subject. Proxy provides the same interface. Decorator provides an enhanced interface. [GoF. p216]

Therefore, since you are restricting the interface this is closer to an Adapter, though we still need to check Bridge and Facade.

If we check Adapter, we get other nuggets:

Bridge is designed up-front to let the abstraction and the implementation vary independently. Adapter is retrofitted to make unrelated classes work together. [GoF, p161]

Facade defines a new interface, whereas Adapter reuses an old interface. Remember that Adapter makes two existing interfaces work together as opposed to defining an entirely new one. [GoF, pp219]

However they are not as telling. At this point it is less clear because the design is not the sole contributor to the name, the intent also matters. A Facade is about hiding complexity and a Bridge is about de-correlating orthogonal dimensions: neither apply here.

Thus we are left with Adapter.