How to convert a JavaScript regex to Swift for email validation?

Question

Hello I am new to Swift, and I am working on a project that requires regex validation for email validation, here's the code

static func validateEmail(string: String?) -> Style.ValidationResult {

    guard let string = string else {
        return .init(
            isValid: false,
            error: ValidationErrors.noEmail
        )
    }

    let format = "^[^!-/[-_{-~]*(?:[0-9A-Za-z](?:[0-9A-Za-z]+|([.])(?!\1)))*([^!-/[-_{-~]){1,256}@[a-zA-Z0-9][a-zA-Z0-9-]{0,64}(\.[a-zA-Z0-9][a-zA-Z0-9-]{0,25})+"
    let predicate = NSPredicate(format: "SELF MATCHES %@", format)
    return .init(
        isValid: predicate.evaluate(with: string),
        error: ValidationErrors.noEmail
    )
}

When I build the app and actually test this part, it either returns Can't do regex matching, reason: Can't open pattern U_REGEX_MISSING_CLOSE_BRACKET or simply cannot build.

I am aware that this is due to the escape character, but I have tried many times and still couldn't find out how to solve it, can anyone tell me the rules to conver JavaScript regex to Swift regex

Does this answer your question? [How to validate an e-mail address in swift?](https://stackoverflow.com/questions/25471114/how-to-validate-an-e-mail-address-in-swift) — Joakim Danielson, Sep 22 '20 at 07:38
In javascript, did you use a `String` or `/.../` pattern? It seems some of the characters need escaping. — Sulthan, Sep 22 '20 at 07:38

score 2 · Accepted Answer · answered Sep 22 '20 at 07:38

You need to

Use a "raw" string literal to avoid double escaping backslashes that form regex escapes (you have \1 backreference and \. regex escape in the pattern), so use let format = #"..."#
You need to escape square brackets inside character classes in an ICU regex pattern because [ and ] are both special (they are used to create character class intersections and unions).

Thus, you need to use

let format = #"^[^!-/\[-_{-~]*(?:[0-9A-Za-z](?:[0-9A-Za-z]+|(\.)(?!\1)))*([^!-/\[-_{-~]){1,256}@[a-zA-Z0-9][a-zA-Z0-9-]{0,64}(?:\.[a-zA-Z0-9][a-zA-Z0-9-]{0,25})+"#

How to convert a JavaScript regex to Swift for email validation?

1 Answers1