Now that we have a good understanding of memory management, we are ready to discuss the full trade-offs we make when we choose to design a type as a structure or a class. With our ability to extend protocols like we saw in the previous chapter, we can achieve very similar functionality to the inheritance we saw with classes in Chapter 3, One Piece at a Time – Types, Scopes, and Projects. This means that we are often choosing between using a structure or a class based on the memory implications, or in other words, whether we want our type to be a value type or a reference type.
Value types have an advantage because they are very simple to reason about. You don't have to worry about multiple variables referencing the same instance. Even better, you don't have to worry about all of the potential problems we have discussed with strong reference cycles. However, there is still an advantage to reference types.
Reference types are advantageous when it really makes sense...