Hi Joshua,
while this is a great idea, I'm afraid that this needs to be more
thought-through. For example, which regex standards would you like to include?
I really hope that Swift's regex support will not get stuck with plain ICU
regexes like NSRegularExpression. I personally would love to see Perl-syntax
improvements such as named groups (any many others):
let regexString = "NS_ENUM\((?P<TYPE>\w+), (?P<NAME>\w+)\)"
let mySource = "NS_ENUM(NSInteger, NSComparisonResult)"
mySource.match("TYPE", in: regexString) // NSInteger
Of course, it would be great if the compiler support could be extended so that
the TYPE and NAME variables can be extracted without using string literals,
e.g. Regex(regexString).firstMatch(in: mySource)?.TYPE
I have written myself an ObjC wrapper arround C++ implementation of such regex
(re2) and use that from Swift instead of using NSRegularExpression.
Regarding your snippet:
- it's always good to keep in mind that in many usecases you only need the
first match, not all of them
- instead of search(_:), consider matches(_:)
- huge part of regex power is in replacing occurrences, which is missing
> On Aug 10, 2017, at 8:25 AM, Joshua Alvarado via swift-evolution
> <[email protected]> wrote:
>
> Hey everyone,
>
> I would like to pitch an implementation of Regex in Swift and gather all of
> your thoughts.
>
> Motivation:
> In the String Manifesto for Swift 4, addressing regular expressions was not
> in scope. Swift 5 would be a more fitting version to address the
> implementation of Regex in Swift. NSRegularExpression is a suitable solution
> for pattern matching but the API is in unfitting for the future direction of
> Swift.
>
> Implementation:
> The Regular expression API will be implemented by a Regex structure object
> which is a regular expression that you can apply to Unicode strings. The
> Regex struct will conform to the RegexProtocol, which is a type that can
> represent a regular expression. ExpressibleByRegexLiteral will be used to
> initialize a regex literal creating an easy to use syntax and a Match
> structure will be used to represent a match found with a Regex.
>
> Draft of implementation:
>
> protocol ExpressibleByRegexLiteral {
> associatedtype RegexLiteralType
>
> init(regexLiteral value: Self.RegexLiteralType)
> }
>
> // Structure of information about a match of regex on a string
> struct Match {
> var regex: Regex
> var start: String.Index
> var end: String.Index
> }
>
> protocol RegexProtocol {
> init(pattern: String) throws
>
> var pattern: String { get } // string representation of the pattern
> func search(string: String) -> Bool // used to check if a match is found
> at all in the string
> func match(string: String) -> [Match] // returns an array of all the
> matches
> func match(string: String, using: ((Match) -> Void)) // enmuerate over
> matches
> }
>
> struct Regex: RegexProtocol {
> init(pattern: Regex, options: Regex.Options)
> let options: [Regex.Options]
> static let word: Regex // \w
> // other useful regexes can be added as well
> }
>
> // Examples
>
> let regex = \[a-zA-Z]+\
> let matches = regex.match("Matching words in text.")
>
> for match in matches {
> print("Found a match at in string at \(match.start) to \(match.end)")
> }
>
> let helloStr = "Hello world"
>
> Regex.word.match(helloStr) { match in
> print("Matched \(helloStr[match.start..<match.end])")
> }
>
> Of course this is a scratch implementation I made but it is to open
> discussion on the topic. I feel the Regex struct itself will need more
> methods and variables such as for flags and number of groups. Please provide
> feedback with improvements to the code, concerns on the topic, or just open
> up discussion. Thank you!
>
> Joshua Alvarado
> [email protected] <mailto:[email protected]>
>
> _______________________________________________
> swift-evolution mailing list
> [email protected]
> https://lists.swift.org/mailman/listinfo/swift-evolution
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