where in Swift

func calculateSize(type: PageType, page: Int) -> Int {
    if type == .Category {
        return defaultPageSize + 1
    }
    else if type == .Detail {
        if page == 1 {
            return defaultPageSize
        }
        else {
            return defaultDetailSize
        }
    }
}

func calculateSize(type: PageType, page: Int) -> Int {
        switch type {
        case .Category:
            return defaultPageSize + 1
        case .Detail where page == 1:
            return defaultPageSize
        default:
            return defaultDetailSize
        }
    }

for number in categories {
    if number != 0 {
        print("\(number)")
    }
}

for number in categories where number != 0 {
    print("\(number)")
}

let numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for number in numbers where number % 2 == 0 {
    print(number)
}

extension Array where Element == Int {
    func printAverageAge() {
        let total = reduce(0, +)
        let average = total / count
        print("Average age is \(average)")
    }
}

let ages = [44, 30, 33, 18, 23]
ages.printAverageAge()

func allItemsMatch<C1: Container, C2: Container>(_ container1: C1, _ container2: C2) -> Bool where C1.Item == C2.Item, C1.Item: Equatable {
    // Implementation here...
    // Check if items in container1 match items in container2
    // ...
    return true // or false
}