Swift Ranges

Swift Ranges

Use ranges to express a sequence of values.

a...b is a closed range including both ends.

a..<b is a half-open range up to but not including b.

Closed and Half-Open

Use a...b for closed ranges (inclusive) and a..<b for half-open ranges (exclusive upper bound).

for n in 1...5 {
      print(n)
    } 
    for n in 1..<5 {
      print(n)
    }
    let r = 10...12
    print(r.contains(11))
    print(r.contains(13))

This example iterates over closed and half-open ranges and checks membership with contains().

One-Sided Ranges

One sided ranges omit one end: ...b starts from the beginning, and a... goes to the end.

let arr = [0, 1, 2, 3, 4]
print(arr[...2])  // first three elements (indices 0...2)
print(arr[2...])  // from index 2 to the end

This example slices an array using one sided ranges: up to and including index 2, and from index 2 to the end.