Automatically update if let and guard let for Swift 5.7

If you've seen the WWDC What's new in Swift? video, you've likely seen the updates to the if let and guard let syntax.

Prior to Swift 5.7, it was common to unwrap an Optional variable and assign to a variable with the same name:

guard let self = self else {
	return
}

if let model = model {
	...
}

Fortunately, this syntax has been simplified in the latest version of Swift. We can now simply re-write these expressions like this:

guard let self else {
    return
}

if let model {
    ...
}

While this is a welcome change, how can we update our entire codebase to reflect this new cleaner syntax? Regular expressions.

You can use the following regular expressions to perform this conversion across your entire codebase.

guard let

Find: guard let (\w+\b) = \b\1\s[else {]

Replace: guard let $1 else {

if let

Find: if let (\w+\b) = \b\1\s[{]

Replace: if let $1 {

This should convert all instances of guard let * = * else and if let * = * to new Swift 5.7 syntax 🚀.

As a bonus, here's a script you can add to your pre-commit hooks to enforce this new convention:

import sys
import re

if __name__ == '__main__':
    arguments = sys.argv
    # The first parameter is always the call to this executable "python3 check-if-let-shorthand" which we can drop
    arguments.pop(0)

    # Searches through all of the modified files verifying the usage of the if-let and guard-let shorthand
    for argument in arguments:
        file = open(argument,  "r")

        text = file.read()
        if_let_pattern = r"if let\s(\w+\b)\s=\s\b\1\s[{]"
        guard_let_pattern = r"guard\slet\s(\w+\b)\s=\s\1\s(else)"

        if len(re.findall(if_let_pattern, text)) > 0 or len(re.findall(guard_let_pattern, text)) > 0:
            print("Invalid if-let or guard-let syntax in " + argument)
            exit(1)

    exit(0)

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