Swift4 NSRange和Range相互转换

Swift中String的一些接口使用Range,不像OC一样使用NSRange,所以使用中就需要把NSRange转换为Range。

extension String {
    func toNSRange(_ range: Range) -> NSRange {
        guard let from = range.lowerBound.samePosition(in: utf16), let to = range.upperBound.samePosition(in: utf16) else {
            return NSMakeRange(0, 0)
        }
        return NSMakeRange(utf16.distance(from: utf16.startIndex, to: from), utf16.distance(from: from, to: to))
    }
    
    func toRange(_ range: NSRange) -> Range? {
        guard let from16 = utf16.index(utf16.startIndex, offsetBy: range.location, limitedBy: utf16.endIndex) else { return nil }
        guard let to16 = utf16.index(from16, offsetBy: range.length, limitedBy: utf16.endIndex) else { return nil }
        guard let from = String.Index(from16, within: self) else { return nil }
        guard let to = String.Index(to16, within: self) else { return nil }
        return from ..< to
    }
}