iOS NSRegularExpression with conditional piece of template - ios

Question

I'm trying to format a phone number to the format (###) ###-####.
I'm using the following regex with replacement template
let regex = try NSRegularExpression(pattern: "([0-9]{3})([0-9]{1,3})([0-9]{0,4})")
regex.stringByReplacingMatches(
in: rawNumber,
options: .reportCompletion,
range: NSRange(location: 0, length: rawNumber.characters.count),
withTemplate: "($1) $2-$3"
)
The problem is that my template string includes the hardcoded - which should not appear if the third capture group $3 isn't found.
For example:
rawNumber = "5125"
would be replaced as (512) 5- when I actually want it in the format (512) 5, because I don't want the - to be shown unless the third capture group was found.
For example I was hoping there might be a way to make a template as something like:
"($1) $2if$3{-}$3"

Answer 1

Without getting fancy, I used the approach of alternate templates in a ternary conditional operator:
let rawNumber = "512512345"
let regex = try NSRegularExpression(pattern: "([0-9]{3})([0-9]{1,3})([0-9]{0,4})")
regex.stringByReplacingMatches(
in: rawNumber,
options: .reportCompletion,
range: NSRange(location: 0, length: rawNumber.characters.count),
withTemplate: "\(rawNumber.count > 6 ? "($1) $2-$3" : "($1) $2")"
)
Result for rawNumber = "5125" is "(512) 5" while rawNumber = "512512345" is "(512) 512-345".
EDIT: Swift 4.2 (and placing result into a constant)
let rawNumber = "512512345"
if let formattedString =
try? NSRegularExpression(pattern: "([0-9]{3})([0-9]{1,3})([0-9]{0,4})", options: []).stringByReplacingMatches(in: rawNumber, options: .reportCompletion, range: NSRange(location: 0, length: rawNumber.count), withTemplate: "\(rawNumber.count > 6 ? "($1) $2-$3" : "($1) $2")") {
print(formattedString)
}

Answer 2

You can write your own subclass of NSRegularExpression for conditional replacement:
class PhoneNumberConverter: NSRegularExpression {
override func replacementString(for result: NSTextCheckingResult, in string: String, offset: Int, template templ: String) -> String {
//Assuming `pattern` has always 3 captures
if result.rangeAt(3).length == 0 {
//$3 isn't found
return super.replacementString(for: result, in: string, offset: offset, template: "($1) $2")
} else {
return super.replacementString(for: result, in: string, offset: offset, template: "($1) $2-$3")
}
}
}
func convertPhoneNumber(rawNumber: String) -> String {
let regex = try! PhoneNumberConverter(pattern: "([0-9]{3})([0-9]{1,3})([0-9]{0,4})")
return regex.stringByReplacingMatches(
in: rawNumber,
options: .reportCompletion,
range: NSRange(location: 0, length: rawNumber.characters.count),
withTemplate: "($1) $2-$3"
)
}
print(convertPhoneNumber(rawNumber: "5125")) //->(512) 5
print(convertPhoneNumber(rawNumber: "512512345")) //->(512) 512-345

Answer 3

Instead of stringByReplacingMatches, use matchesInString. This will give you the list of matches (there should be only one), which itself contains the list of the ranges for each capturing group.
You can then check which capturing group did actually match, and from there, use one template or the other.

Answer 4

It looks like there is no way to do this as all of the template string is interpreted as literal characters except for the capture groups.
https://developer.apple.com/reference/foundation/nsregularexpression: