All variables and constants in Swift are stored in memory. In fact, unless you explicitly write data to the file system, everything you create is going to be in memory. In Swift, there are two different categories of types. These two categories are value types and reference types. The only way in which they differ is in the way they behave when they get assigned to new variables, passed into methods, or captured in closures. Essentially, they only differ when you try to assign a new variable or constant to the value of an existing variable or constant.
A value type is always copied when being assigned somewhere new while a reference type is not. Before we look at exactly what that means in more detail, let's go over how we determine if a type is a value type or a reference type.