Code used for my tutorial "Embracing the Swift Standard Library" (https://www.andyibanez.com/embracing-the-swift-standard-library)

Making Swift Objects Behave Like an Array

struct ShoppingItem {
    let name: String
    let price: Float
    
    init(name: String, price: Float) {
        self.name = name
        self.price = price
    }
}

struct ShoppingList : SequenceType, GeneratorType, ArrayLiteralConvertible {
    
    private let items: [ShoppingItem]
    
    var count: Int {
        get {
            return items.count
        }
    }
    
    var total: Float {
        get {
            var total: Float = 0
            for item in self.items {
                total += item.price
            }
            return total
        }
    }
    
    var average: Float {
        get {
            return self.total / Float(self.count)
        }
    }
    
    subscript(index: Int) -> ShoppingItem {
        return self.items[index]
    }
    
    /// MARK: - ArrayLiteralConvertible
    
    init(arrayLiteral: ShoppingItem...) {
        self.items = arrayLiteral
    }
    
    /// MARK: - SequenceType
    
    typealias Generator = ShoppingList
    
    func filter(includeElement: (ShoppingItem) -> Bool) -> [ShoppingItem] {
        var fItems = [ShoppingItem]()
        for itm in self.items where includeElement(itm) == true {
            fItems += [itm]
        }
        return fItems
    }
    
    func generate() -> Generator {
        return self
    }
    
    /// MARK: - GeneratorType
    
    var currentElement = 0
    
    mutating func next() -> ShoppingItem? {
        if currentElement < self.items.count {
            let curItem = currentElement
            currentElement++
            return self.items[curItem]
        }
        return nil
    }
    
}


let apples = ShoppingItem(name: "Apples", price: 12.76)
let carrots = ShoppingItem(name: "Carrots", price: 15.43)
let bananas = ShoppingItem(name: "Bananas", price: 32.53)

let shoppingList: ShoppingList = [apples, carrots, bananas]

print("All items in my list:")
for item in shoppingList {
    print("\(item.name) cost \(item.price)")
}

print("Only items that cost under 13:")
for item in shoppingList where item.price < 13 {
    print("\(item.name) cost \(item.price)")
}