SergBarkovskii

/*:
 ## Exercise: Leap Years
 
 To decide if a year is a leap year, there are several decisions that have to be made:
 
 - Is the year divisible by 4?
    - If so, is the year divisible by 100?
        - If not, it is a leap year.
        - If so, is the year divisible by 400?
            - If not, it is **not** a leap year.

SergBarkovskii

Protocols and Extensions
Use protocol to declare a protocol.

protocol ExampleProtocol {
     var simpleDescription: String { get }
     mutating func adjust()
}

Classes, enumerations, and structs can all adopt protocols.