A version of NSString's stringByAppendingPathComponent that's readily available on Swift.String. This implementation uses Foundation (hence the Bridged file name). This

BridgedSwiftStringByAppendingPaths.swift

import Swift
import Foundation

extension String {
    /// WARNING: Unless `paths.isEmpty`, the resultant String is always backed by NSString storage.
    init(basePath: String, paths: [String]) {
        guard paths.count > 0 else {
            self = basePath; return
        }
        
        self = paths
            .reduce(basePath as NSString, combine: { combined, each in
                return combined.stringByAppendingPathComponent(each)
            })
            as String
    }
    
    init(basePath: String, paths: String...) {
        self.init(basePath: basePath, paths: paths)
    }
}