Swift Strings

let name = "Sam"
let items = 3
print("Hi \(name), you have \(items) items")
print("Next year you'll be \(age + 1)")

• Write \( then any value or expression, then ) inside a string, and Swift inserts its value.
• Numbers, Bools and other types are converted to text automatically.
• You can also join strings with +, but interpolation is clearer and doesn't need conversions.
• Special characters use a backslash: \n for a new line, \" for a quote, \\ for a backslash.

• text.count is the number of characters; text.isEmpty checks for "".
• text.first and text.last are optional Characters (nil for an empty string).
• text.prefix(3) and text.suffix(3) give the first and last three characters; dropFirst() and dropLast() remove some from the ends.
• for ch in text { } loops over every character.
• text.reversed() gives the characters backwards; wrap it in String(...) to get a String.

Results like prefix are a Substring, a lightweight view into the original string. Convert with String(sub) when you store it or pass it to code that expects a String.

Methods marked Foundation need import Foundation at the top of the file. In an app, SwiftUI and UIKit import it for you.

split(separator: ",") breaks a string into an array of Substrings, and joined(separator: ", ") joins an array of strings back together:

let tags = "swift,ios,xcode".split(separator: ",")
print(tags.joined(separator: " | "))   // swift | ios | xcode

A multi-line string starts and ends with three double quotes on their own lines. Indentation before the closing quotes is removed from every line, so you can keep code tidy:

let email = """
    Dear \(name),
    Your order has shipped.
    """

Characters in Swift can take different amounts of memory. A plain "e" is one byte in UTF-8, "é" is two, and a flag emoji is eight, yet each counts as one Character:

let word = "café"
print(word.count, word.utf8.count)      // 4 5

Because of this, Swift can't jump straight to "character number 2"; it has to walk through the string from the start. Rather than hide that cost behind text[2], Swift makes you ask for a position explicitly with a String.Index:

let text = "Swift"
let i = text.index(text.startIndex, offsetBy: 2)
print(text[i])                             // i
if let f = text.firstIndex(of: "f") {
    print(text[..<f])                      // Swi
}

In practice you rarely need indexes. prefix, suffix, first, contains and split cover most everyday jobs. If you find yourself indexing heavily, converting to an array with Array(text) gives you integer positions at the cost of a copy.

< and > compare strings character by character, using Unicode values. All capital letters come before all lower-case ones, so "Zebra" < "apple" is true. To sort the way people expect, compare lower-cased copies:

let fruit = ["pear", "Apple", "banana"]
print(fruit.sorted { $0.lowercased() < $1.lowercased() })
// ["Apple", "banana", "pear"]

A raw string is wrapped in #" and "#. Backslashes and quotes inside it are taken literally, which is handy for file paths and regular expressions. Interpolation still works if you add the hash: #"Total: \#(n)"#.