trim.swift

internal extension CollectionType where Index: BidirectionalIndexType {
    internal func _lastIndexOf(@noescape isElement: Generator.Element -> Bool) -> Index? {
        for i in indices.reverse()
            where isElement(self[i]) {
                return i
        }
        return nil
    }
}

internal extension CollectionType where Index: BidirectionalIndexType, Generator.Element: Equatable {
    internal func _lastIndexOf(element: Generator.Element) -> Index? {
        return _lastIndexOf { e in e == element }
    }
}

public extension String {
    /// Retake on "lastPathComponent" and "pathExtension"
    /// but a little more general in behavior
    ///
    /// - Authors: aciidb, erica, oisdk, with space-assist from jweinberg
    public func suffixFrom(
        boundary: Character,
        searchingBackwards backwards: Bool = true,
        includingBoundary include: Bool = false) -> String {
            guard let i = backwards ?
                characters._lastIndexOf(boundary) :
                characters.indexOf(boundary)
                else { return self }
            return String(characters.suffixFrom(include ? i : i.successor()))
    }
    
    /// Alternative to lastPathComponent, pathExtension
    /// but taking prefix instead of suffix
    ///
    /// - Authors: aciidb, erica, oisdk, with space-assist from jweinberg
    public func prefixTo(
        boundary: Character,
        searchingForwards forwards: Bool = true,
        includingBoundary include: Bool = false) -> String {
            guard let i = forwards ?
                characters.indexOf(boundary) :
                characters._lastIndexOf(boundary)
                else { return self }
            return String(include ? characters.prefixThrough(i) : characters.prefixUpTo(i))
    }
}