Enumerations share many features with classes and structures

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Enums in Swift are much more powerful than some of their counterparts in other languages, such as C. They share many features with classes and structs, such as defining initialisers, computed properties, instance methods, protocol conformances and extensions.

protocol ChangesDirection {
    mutating func changeDirection()
}

enum Direction {
    
    // enumeration cases
    case up, down, left, right
    
    // initialise the enum instance with a case
    // that's in the opposite direction to another
    init(oppositeTo otherDirection: Direction) {
        self = otherDirection.opposite
    }
    
    // computed property that returns the opposite direction
    var opposite: Direction {
        switch self {
        case .up:
            return .down
        case .down:
            return .up
        case .left:
            return .right
        case .right:
            return .left
        }
    }
}

// extension to Direction that adds conformance to the ChangesDirection protocol
extension Direction: ChangesDirection {
    mutating func changeDirection() {
        self = .left
    }
}

var dir = Direction(oppositeTo: .down) // Direction.up

dir.changeDirection() // Direction.left

let opposite = dir.opposite // Direction.right

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