Swift Ranges

Ranges are generic Swift Structures for selecting a range, or a limited subset, of an existing type. Ranges are used commonly for identifying elements between the lowest and highest values in a set.

Kinds of Ranges

Swift gives us two ways of creating ranges. Half-Open range, and Closed Range.

Half-Open Range

The Half-Open range operator is declared with ..< between a numeric pair. Using a Range instance, you can quickly check to see if a value is contained in a particular range of values. This creates a range up to but not including the upper bound value.

let underFive = 0.0..<5.0
underFive.contains(3.14) // true
underFive.contains(6.28) // false
underFive.contains(5.0) // false (upper bound value not included)

Range instances can represent an empty interval, unlike Closed Range(see below.)

let empty = 0.0..<0.0
empty.contains(0.0) // false
empty.isEmpty // true

Range can also be used to specify a collection of consecutive, strideable values, usually Integers. It can also be used in for-in loops or with any sequence or collection method. The results of the range include all values up to, but not including the upperBound.

for n in 3..<5 {
  print(n)
}
// prints "3"
// prints "4"
// does NOT print "5"

Ranges help in Switch statements, using them for your cases. Consider the following:

let score = 92

switch score {
  case 0..<50:
    print("Fail")
  case 50..<90:
    print("Pass")
  default:
    print("Excellent")
} // prints "Excellent"

Closed Range

A Closed range operator is declared with ... between a pair of numeric values. The left value being the lowerBound and the right value being upperBound. The Closed Range includes the upperBound value.

let range : ClosedRange = 0...5
print(range) // 0...5
print(range.first) // Optional(0)
print(range.last) // Optional(10)

for index in range {
  print(index) // prints consecutivly, values from 0 to 5
}

Inspecting a Range

Here are just a few of the operations you can call on a range instance in Swift. There are many more in Apple's Documentation for Range.

var isEmpty: Bool

Returns a Boolean value indicating whether the range contains no elements.

var count: Int

Returns the number of elements in the collection of values.

let lowerBound: Bound

Returns the range's lower bound

let upperBound: Bound

Returns the range's upper bound

That's it for this quick post. See you in the next one.