Classes and Structures

Classes have additional capabilities that structures do not

• Inheritance enables one class to inherit the characteristics of another.
• Type casting enables you to check and interpret the type of a class instance at runtime.
• Deinitializers enable an instance of a class to free up any resources it has assigned.
• Reference counting allows more than one reference to a class instance.

Structures are always copied when they are passed around in your code, and do not use reference counting.

Value Types vs Reference Types

A value type is a type whose value is copied when it is assigned to a variable or constant, or when it is passed to a function. In fact, all of the basic types in Swift—integers, floating-point numbers, Booleans, strings, arrays and dictionaries—are value types, and are implemented as structures behind the scenes.

Unlike value types, reference types are not copied when they are assigned to a variable or constant, or when they are passed to a function. Rather than a copy, a reference to the same existing instance is used instead.

Identity Operators

How to define an abstract class