Structs - Part O

// STRUCTS (Part I)

// Struct with one "stored" property
struct Sport {
    var name: String
}

var tennis = Sport(name: "Tennis")
print(tennis.name)

// tennis and name are variables, so they can be changed
tennis.name = "Lawn Tennis"

// COMPUTED PROPERTIES
// New struct with two stored properties
// and one computed property:
// NB: Constants cannot be computed properties
struct Sport2 {
    var name: String
    var isOlympicSport: Bool

    var olympicStatus: String  {
        if isOlympicSport {
            return "\(name) is an Olympic sport"
        } else {
            return "\(name) is not an Olympic sport"
        }
    }
}
let taiChi = Sport2(name: "Tai Chi", isOlympicSport: false)
taiChi.olympicStatus    // "Tai Chi is not an Olympic sport"

// PROPERTY OBSERVERS
// willSet{}: Used before a property is changed
// didSet{}: Used after a property is changed
struct Progress {
    var amount: Int {
        willSet {
            print("Progress is about to change.")
        }
        didSet {
            print("Progress is now \(amount) percent")
        }
    }
}

var progress = Progress(amount: 20)
print(progress.amount)      // "20"
progress.amount = 40        // "Progress is about to change."
                            // "Progress is now 40 percent"

// METHODS
// Functions inside Structs are called methods
struct City {
    var population: Int

    func collectTaxes() -> Int {
        return population * 1000
    }
}

let smallCity = City(population: 10_000)
print("We can collect \(smallCity.collectTaxes()) in taxes!")

// MUTATING METHODS
// Swift won't allow a struct's method to change it's associated properties,
// unless the "mutating func" keywords are used
struct Person {
    var name: String

    mutating func changeNameToFred() {
        name = "Fred"
    }
}

var jim = Person(name: "Jim")
jim.changeNameToFred()
jim.name                // "Fred"

// PROPERTIES AND METHODS OF STRINGS
// Strings are structs!
// And have their own properties and methods
let string = "Do or do not, there is no try."

// count property
string.count

// various methods:
string.hasPrefix("Do")          // return true
string.uppercased()             // everything now uppercased
string.sorted()                 // returns array

// PROPERTIES AND METHODS OF ARRAYS
// Arrays aare also structs!
// Yep, they've got their own properties and methods
var beatles = ["John", "Paul", "George", "Ringo"]

// count property
beatles.count

// add new item method
beatles.append("Fifth Beatle")

// locate item method
beatles.firstIndex(of: "John")

// sort method
beatles.sorted()

// remove item method
beatles.remove(at: 0)