دلالات فهارس ArraySlice

تحتفظ الشرائح بالفهرسة الأصلية

let arr = [10, 20, 30, 40, 50]
let slice = arr[2..<5]
print(slice.startIndex)
print(slice.endIndex)

لا يكون startIndex صفرًا دائمًا

let arr = [1, 2, 3, 4, 5, 6]
let slice = arr[3..<6]
print("start:", slice.startIndex)
print("first value:", slice[slice.startIndex])

الفهرسة في شريحة

let arr = [100, 200, 300, 400]
let slice = arr[2..<4]
print(slice[2])
print(slice[3])

استخدام startIndex بأمان

let arr = [5, 6, 7, 8, 9]
let slice = arr[2..<5]
print(slice.first ?? -1)
print(slice[slice.startIndex])

يشير endIndex إلى ما بعد الأخير

let arr = [11, 22, 33, 44]
let slice = arr[1..<3]
print("endIndex:", slice.endIndex)
print("last valid:", slice[slice.endIndex - 1])

العد مقابل الفهرسة

let arr = [0, 1, 2, 3, 4, 5]
let slice = arr[3..<6]
print("count:", slice.count)
print("startIndex:", slice.startIndex)

خاصية indices

let arr = [10, 20, 30, 40, 50]
let slice = arr[1..<4]
for i in slice.indices {
    print(i, slice[i])
}

سبب الاحتفاظ بالفهرسات

let arr = ["a", "b", "c", "d", "e"]
let slice = arr[2..<5]
if let idx = slice.firstIndex(of: "d") {
    print("found at parent index:", idx)
    print("parent has:", arr[idx])
}

يعيد enumerate الترقيم إلى الصفر

let arr = [9, 8, 7, 6, 5]
let slice = arr[2..<5]
for (offset, value) in slice.enumerated() {
    print(offset, value)
}

المسافة من البداية

let arr = [1, 2, 3, 4, 5]
let slice = arr[2..<5]
let idx = slice.startIndex + 1
let offset = slice.distance(from: slice.startIndex, to: idx)
print("offset:", offset, "value:", slice[idx])

خطأ شائع

let arr = [100, 200, 300, 400, 500]
let slice = arr[3..<5]
// Safe: use first, not slice[0]
print(slice.first ?? 0)

تحقق سريع

مراجعة

let slice = [5, 6, 7, 8, 9][3..<5]
print(slice.startIndex, slice.first ?? -1)