Swift Ranges

In Swift, a range is a series of values between two numeric intervals. For example,

var numbers = 1...4

Here,

• ... is a range operator
• 1...4 contains values 1, 2, 3, 4
• 1 is lower bound (first element)
• 4 is upper bound (last element)

Types of Range in Swift

In Swift, there are three types of range:

• Closed Range
• Half-Open Range
• One-Sided Range

1. Closed Range

A closed range includes all the values in the interval from the lower bound to the upper bound.

It is declared using the ... (3 dots) operator. For example,

// 1...4 is close range
for numbers in 1...4 {
  print(numbers)
}

Output

1
2
3
4

In the above example, we have created a closed range 1...4.

Since it is a closed range, it contains all the numbers between 1 to 4 including the lower bound (1) and upper bound (4).

Here, we have used the Swift for loop to access all the values in the range.

2. Half-Open Range

A half-open range includes all the values from the lower bound to the upper bound. However, it excludes the upper bound (last number).

It is declared using the ..< operator. For example,

for numbers in 1..<4 {
  print(numbers)
}

Output

1
2
3

In the above example, we have created a half-open range 1..<4. Since it is a half-open range, it excludes the upper bound element 4.

3. One-sided Range

We can create a one-sided range using either of the ... or the ..< operator.

A one-sided range contains elements up to infinite in one direction. For example,

let range1 = ..<2

Here, ...<2 is a one-sided range. It contains all elements from 2 to -∞. Similarly, the range

let range2 = 2...

contains all elements from 2 to +∞.

We can verify this by checking if a certain number is present in the range. For example,

// one-sided range using 
// ..< operator
let range1 = ..<2

// check if -9 is in the range
print(range1.contains(-1))

// one-sided range using
// ... operator
let range2 = 2...

// check if 33 is in the range
print(range2.contains(33))

Output

true
true

Here, we have used contains() method to check if a certain number is present in the range.

Note: With a one-sided range, we only set either upper bound or lower bound.

Access Array Elements Using Swift Range

We can also use the Swift range to access array elements. For Example,

let languages = ["Swift", "Java", "C"]

// access array elements
print(languages[0...2]) 

Output

["Swift", "Java", "C"]

Here, the range 0...2 acts as array indices and helps us access all array elements.

Things to Remember About Swift Range

1. The lower bound value must be smaller than the upper bound value. For example,

// Invalid Range
3...1

// Valid Range
1...3

2. The lower bound and upper bound value can be negative. For example,

// negative lower bound
-3...1

// negative upper and lower bound
-9...-2