NSRegularExpression initializer fails to compile in Swift 4.2

Question

Created Oct ’18

Replies 3

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Views 2.7k

Participants 3

In swift 4.2 I am trying to write the following code:

let regex = NSRegularExpression(
pattern: "\w[A-Z]",
options: NSRegularExpression.Options.allowCommentsAndWhitespace
)

This initializer shows up in the autocomplete, but when I try to build, I get the following 2 errors:

- Incorrect argument label in call (have 'options:', expected 'coder:')

- Invalid escape sequence in literal

It seems like a bug, but I could also be doing something wrong!

Answered by samjohn in 337096022

Solved!

1. The problem was in the xcode autocomplete, for swift 4.2 the API is actually

NSRegularExpression(pattern: "")

2. The invalid escape sequence was due to needing to escape the backslash.

So the following works:

let regex = try NSRegularExpression(pattern: "\\w[A-Z]")

Boost

Answer 1

samjohn OP

Oct ’18

Accepted Answer

Solved!

1. The problem was in the xcode autocomplete, for swift 4.2 the API is actually

NSRegularExpression(pattern: "")

2. The invalid escape sequence was due to needing to escape the backslash.

So the following works:

let regex = try NSRegularExpression(pattern: "\\w[A-Z]")

0

Answer 2

OOPer OP

Oct ’18

It's because you are not writing a String literal correctly.

When you want to pass \w to NSRegurlarExpression, the character \ needs to be escaped.

do {
    let regex = try NSRegularExpression(
        pattern: "\\w[A-Z]",
        options: NSRegularExpression.Options.allowCommentsAndWhitespace
    )
    //Use `regex` ...
} catch {
    print(error)
}

Seems you found it yourself. By the way, both `NSRegularExpression.init(pattern:)` and `NSRegularExpression.init(pattern:options:)` are valid.

0

Answer 3

DTS Engineer OP

Apple

Oct ’18

It's because you are not writing a String literal correctly.

FYI, a future Swift will make this easier by way of SE-0200 Enhancing String Literals Delimiters to Support Raw Text. Alas, this is not in Swift 4.2.

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