Monday, December 19, 2016 [Tweets] [Favorites]

NSRegularExpression and Swift

Nate Cook:

Well, many NSRegularExpression methods use NSRanges, as do the NSTextCheckingResult instances that store a match’s data. NSRange, in turn, uses integers for its location and length, while none of String’s views use integers as an index[…]

[…]

With that in mind, here are a few additions to String that will make straddling the Swift/Objective-C divide a bit easier:

extension String {
    /// An `NSRange` that represents the full range of the string.
    var nsrange: NSRange {
        return NSRange(location: 0, length: utf16.count)
    }

    /// Returns a substring with the given `NSRange`, 
    /// or `nil` if the range can't be converted.
    func substring(with nsrange: NSRange) -> String? {
        guard let range = nsrange.toRange() 
            else { return nil }
        let start = UTF16Index(range.lowerBound)
        let end = UTF16Index(range.upperBound)
        return String(utf16[start..<end])
    }

    /// Returns a range equivalent to the given `NSRange`,
    /// or `nil` if the range can't be converted.
    func range(from nsrange: NSRange) -> Range<Index>? {
        guard let range = nsrange.toRange() else { return nil }
        let utf16Start = UTF16Index(range.lowerBound)
        let utf16End = UTF16Index(range.upperBound)

        guard let start = Index(utf16Start, within: self),
            let end = Index(utf16End, within: self)
            else { return nil }

        return start..<end
    }
}

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