head-first-design-patterns | repository containing all the Head First Design | Architecture library

PizzaStore class already contains a SimplePizzaFactory object

Well, PizzaStore have a non-initialized attribute of type SimplePizzaFactory. In the PizzaStore constructor, that attribute is initialized with a reference to the constructor argument. This is an usual pattern in Java code.

The passed-on object is not initialized with any data (which needs to be copied by PizzaStore Constructor)

There is no need to add initialization code in the constructor, is asumed that the SimplePizzaFactory is already initialized. That factory is not copied, is referenced by the PizzaStore attribute, so the factory inside the PizzaStore, after the constructor is executed, is an already initialized object.

There's some overlap:

• GoF Subject: Subscribe handler, unsubscribe handler, send notification to handlers

• Rx Observable: Subscribe handler of type T, (implicitly unsubscribe via subscription disposable)

• Rx Observer: Handler that receives notification of type T (or error, or end)
• Rx Subject: Observable + Observer for some type T

So they support the same basic operations. I would assume Rx Team chose their name based on GoF usage. Rx Team though clearly wanted to split the functions of 'Subject' into sender and receiver: The emphasis in Rx is observables, not subjects.

Arbitrary objects are can not be tested for equality. There are many kinds of objects which full equality is difficult or even impossible to determine in Swift (and generally speaking in most popular languages; Swift just addresses this problem more explicitly than many other languages do). There are lots of ways to address this, but in your case you really likely mean that the observer is some specific instance of a class, a reference type, rather than a value. The number 4 is probably not allowed to be an observer, for instance. That's something that can happen in Swift, so you need to tell Swift that it isn't legal here because 4 is a value, not a reference.

OK, enough background. How do you do it? Well, first, say Observers have to be classes (i.e. reference types).