Ranges

Ranges are used to create an interval of values. There are two kinds of range structures, Range for creating half-open ranges and ClosedRange for creating closed ranges.

Creating Ranges

Half-open Ranges

Range instances are declared using the ..< half-open range operator. They include values from a lower bound up to, but excluding an upper bound.

The syntax below shows how to create a half-open range with lower as the lower bound value and upper as the upper bound value:

let newRange = lower..<upper

Closed Ranges

ClosedRange instances are declared using the ... closed range operator. They contain values from a lower bound up to and including an upper bound.

The syntax below shows how to create a closed range with lower as the lower bound value and upper as the upper bound value:

let newClosedRange = lower...upper

Using Ranges

Some useful applications of ranges are:

• For iteration with for-in loops.
• In switch statements to find out if a value lies within an interval.
• Selecting a section of an array.

For-in Loop Example

The example below uses for-in loops with a half-open range and then a closed range to print some emoji trees:

for n in 1..<4 {
  print(String(repeating: "🌲", count: n))
}

for n in 1...4 {
  print(String(repeating: "🌳", count: n))
}

The above example will result in the following output:

🌲
🌲🌲
🌲🌲🌲
🌳
🌳🌳
🌳🌳🌳
🌳🌳🌳🌳

Switch Example

The example below uses a switch statement and a closed range to determine which emoji to print depending on the value of treeHeight:

let treeHeight = 2

switch treeHeight {
case 0...30:
    print("🌱")
default:
     print("🌳")
}

The above example will result in the following output:

🌱

Array Example

The example below prints out a section of the tree array using a closed range to select the element indexes:

let trees = ["Pine", "Oak", "Ash", "Willow", "Olive"]

print(trees[2...4])

The above example will result in the following output:

["Ash", "Willow", "Olive"]