Klausa where pada ekstensi

Mengapa perluasan berbatasan?

Perluasan tipe dengan batasan

extension Array where Element: Equatable {
    func removing(_ value: Element) -> [Element] {
        filter { $0 != value }
    }
    func containsAll(_ others: [Element]) -> Bool {
        others.allSatisfy(self.contains)
    }
}
print([1,2,3].removing(2))        // [1,3]
print(["a","b"].containsAll(["b"])) // true

Perluasan protokol dengan where

extension Collection where Element: Comparable {
    var isSorted: Bool {
        // Pair each element with the next; ensure non-decreasing order
        zip(self, dropFirst()).allSatisfy(<=)
    }
}
print([1,2,3].isSorted)     // true
print([3,1,2].isSorted)     // false

Batasan pencocokan tepat

extension Collection where Element == Int {
    var sum: Int { reduce(0, +) }
    func average() -> Double {
        isEmpty ? 0 : Double(sum) / Double(count)
    }
}
print([1,2,3].sum)          // 6
print([1,2,3].average())    // 2.0

API berbasis kemampuan

extension Collection where Element: Numeric {
    var total: Element { reduce(0, +) }
}
extension Sequence where Element: Hashable {
    var uniques: [Element] {
        var seen = Set<Element>()
        return filter { seen.insert($0).inserted }
    }
}
print([1,2,2,3].uniques)    // [1,2,3]
print([1,2,3].total)        // 6

Catatan desain

Tujuan ekstensi terbatas

Ringkasan