Working with Strings

Strings come with many built-in properties and methods. A few more come from Foundation, Apple's standard library of utilities — add import Foundation at the top of the file to use them (it's available on every platform Swift runs on).

Example

import Foundation

let text = "  Hello, Swift World  "
let trimmed = text.trimmingCharacters(in: .whitespaces)

print(trimmed)
print(trimmed.uppercased())
print(trimmed.lowercased())
print(trimmed.count)
print(trimmed.hasPrefix("Hello"))
print(trimmed.hasSuffix("!"))
print(trimmed.contains("Swift"))
print(trimmed.replacingOccurrences(of: "World", with: "Friends"))
print("a,b,c".split(separator: ","))
print(String("Swift".reversed()))
print("".isEmpty)

Expected output

Hello, Swift World
HELLO, SWIFT WORLD
hello, swift world
18
true
false
true
Hello, Swift Friends
["a", "b", "c"]
tfiwS
true

Methods like uppercased() return a new string — the original is unchanged. Strings in Swift are values, not shared objects.

Characters and Unicode

Swift strings handle every language and emoji correctly. count counts characters as a person would see them:

print("café".count)
print("👍🏽".count)

for letter in "Hi!" {
    print(letter)
}

4
1
H
i
!

That thumbs-up with a skin tone is several Unicode code points, but one character — which is what Swift counts.

Getting characters by position

Because characters can take different amounts of memory, Swift strings can't be indexed with a plain number like text[0]. Use first, last, prefix, and dropFirst, or convert to an array:

let word = "Swift"
print(word.first!)
print(word.prefix(3))
print(word.dropFirst(2))
print(Array(word)[1])

S
Swi
ift
w

(The ! after first is explained in the Optionals lessons — first could be missing if the string were empty.)

Common mistakes

• Writing text[0] — 'subscript(_:)' is unavailable: cannot subscript String with an Int. Use first, prefix, or Array(text).
• Forgetting import Foundation for methods like trimmingCharacters(in:) and replacingOccurrences(of:with:).

Practice

Given let email = " Ada@Example.COM ", print it trimmed and in lowercase.

import Foundation

let email = "  Ada@Example.COM "
print(email.trimmingCharacters(in: .whitespaces).lowercased())

ada@example.com