Find, range

A string exists within another string. We could use a complicated loop to find it. This is hard to write and maintain.

With range, we can locate a string. A range is returned if the string is found. If nothing is found, we receive an empty optional. We use an if-let construct to test the result of range().

An example

Our string has the 4 words "a soft orange cat." It is a nice cat. We include Foundation at the top of the Swift file. We call range() next and search for "orange."

import Foundation

// Input string.
let line = "a soft orange cat"

// Search for one string in another.
var result = line.range(of: "orange",
                        options: NSString.CompareOptions.literal,
                        range: line.startIndex..<line.endIndex,
                        locale: nil)

// See if string was found.
if let range = result {

    // Start of range of found string.
    let start = range.lowerBound

    // Display string starting at first index.
    print(line[start..<line.endIndex])

    // Display string before first index.
    print(line[line.startIndex..<start])
}
orange cat
a soft

Contains

Here we invoke a method called "contains." We call this method on the string "abc123abc." This returns true or false. If the argument exists in the string, it returns true.

import Foundation

let value = "abc123abc"

// See if the string contains the argument string.
let result1 = value.contains("23a")
print(result1)

// This substring does not exist.
let result2 = value.contains("def")
print(result2)
true
false

With Swift, a specific method is often the easiest way of testing a string. Here contains() is often a good choice. For indexes, though, range() with an "of" argument is effective.

Some notes

In Swift we must address string characters through ranges. To see where a string exists in another, we must use ranges. And with optionals, we test for existence.