To some, it may seem surprising that protocols are considered a type, since we cannot actually create an instance of them; however, we can use them as a type. What we mean by this statement is that when we define the type for a variable, constant, tuple, or collection, we can use a protocol for that type.
We are not going to cover protocols in depth in this section, since we have a whole chapter dedicated to them however it is important to understand that they are considered a type in Swift.
Each type that we have discussed so far is either a value or a reference type; however, a protocol is neither because we are not able to create an instance of them.
It is really important to have a complete understanding of the difference between value and reference types in Swift, so let's compare the two.