Proxy or decorator?

transcript

Two classes. Both have exactly the same interface as the object they wrap. One is a proxy. One is a decorator. The code looks almost identical. So how do you tell them apart?

A proxy controls access to the real object. Create it later, check who is asking, remember an answer. A decorator adds a responsibility. A retry. A log line. A surge fee.

Look at who builds what. A proxy often creates and owns the real object itself. A decorator is chosen by the client, and stacked in any order. The book says a protection proxy can look exactly like a decorator.

The third look-alike is different. An adapter changes the interface, so a class you can't edit still fits. A proxy and a decorator both keep the interface the same. That's why purpose decides.

Is it access, a new duty, or translation? So ask what the wrapper is for.

Full breakdown in the lecture.