Swift - String Replace Example

Replace. In Swift 5.8, we can change ranges of characters in strings. With replaceSubrange we can replace them with another string. We use index() to create a range.

When replacing strings in Swift, we often combine multiple methods. We combine index() and replacement methods like replaceSubrange.

Example program. In this program we first declare a string. This string has a substring "red" in it. We next call replaceSubrange with a range.

Here We pass a range to replaceSubrange. We use index() on the string to get the bounds. We advance 6 chars.

Also We use a range operator to advance to 9 chars into the string. We base the end also on the startIndex.

Range

Result ReplaceSubrange changes the string "red" in the string to "yellow." The string remains colorful.

var value = "green red blue"
print(value)

// Replace range at positions 6 through 9.
// ... Specify a replacement string.
let start = value.index(value.startIndex, offsetBy: 6);
let end = value.index(value.startIndex, offsetBy: 6 + 3);
value.replaceSubrange(start..<end, with: "yellow")
print(value)green red blue
green yellow blue

Change chars. This program loops through the chars in a string. It then uses an if-else block to change some chars in the string. The value "1" is changed.

for

Tip This approach can be used to translate chars in a string. A more complex data structure (dictionary) could be used.

Dictionary

Info Append() adds a char to a string. We build up a new string in the for-loop.

var value = "123abc123"
var result = String()

// Replace individual characters in the string.
// ... Append them to a new string.
for char in value {
    if char == "1" {
        let temp: Character = "9"
        result.append(temp)
    }
    else {
        result.append(char)
    }
}

print(result)
923abc923

ReplacingOccurrences. In Foundation we find some string replacement methods. With replacingOccurrences we replace all occurrences of one substring with another.

Here We change the word "cats" to "birds." This might make the "dogs" part happier.

import Foundation

let text = "cats and dogs"

// Replace cats with birds.
// ... Use Foundation method.
let result = text.replacingOccurrences(of: "cats", with: "birds")

// Print result.
print(result)
birds and dogs

ReplacingCharacters. Here we use replacingCharacters. This may have the same effect as the replaceSubrange method in Swift. It replaces a range with a substring.

import Foundation

let letters = "ZZZY"
// Replace first 3 characters with a string.
let start = letters.startIndex;
let end = letters.index(letters.startIndex, offsetBy: 3);
let result = letters.replacingCharacters(in: start..<end, with: "WH")
// The result.
print(result)
WHY

Strings in Swift are accessed through ranges, along with startIndex and endIndex. To replace chars, we access a range and invoke replaceSubrange.