Using NSFileManager contentsOfDirectoryAtPath in Swift, with tuple result and CPS interfaces

contentsOfDirectoryAtPath.swift

import Foundation


// Tuple result

// Get contents of directory at specified path, returning (filenames, nil) or (nil, error)
func contentsOfDirectoryAtPath(path: String) -> (filenames: String[]?, error: NSError?) {
    var error: NSError? = nil
    let fileManager = NSFileManager.defaultManager()
    let contents = fileManager.contentsOfDirectoryAtPath(path, error: &error)
    if contents == nil {
        return (nil, error)
    }
    else {
        let filenames = contents as String[]
        return (filenames, nil)
    }
}

let (filenamesOpt, errorOpt) = contentsOfDirectoryAtPath("/Users")
if let filenames = filenamesOpt {
    filenames               // [".localized", "kris", ...]
}

let (filenamesOpt2, errorOpt2) = contentsOfDirectoryAtPath("/NoSuchDirectory")
if let err = errorOpt2 {
    err.description         // "Error Domain=NSCocoaErrorDomain Code=260 "The operation couldn’t be completed. ... "
}


// Continuation Passing Style (CPS) interface

// Get contents of directory at specified path, invoking block with (filenames, nil) or (nil, error)
func getContentsOfDirectoryAtPath(path: String, block: (filenames: String[]?, error: NSError?) -> ()) {
    var error: NSError? = nil
    let fileManager = NSFileManager.defaultManager()
    let contents = fileManager.contentsOfDirectoryAtPath(path, error: &error)
    if contents == nil {
        block(filenames: nil, error: error)
    }
    else {
        let filenames = contents as String[]
        block(filenames: filenames, error: nil)
    }
}

getContentsOfDirectoryAtPath("/Users") { (result, error) in
    if let e = error {
        e.description
    }
    else if let filenames = result {
        filenames                     // [".localized", "kdj", ... ]
    }
}

getContentsOfDirectoryAtPath("/NoSuchDirectory") { (result, error) in
    if let e = error {
        e.description                // "Error Domain=NSCocoaError..."
    }
    else if let filenames = result {
        filenames
    }
}

// Do something with the files in my home directory
let listMyFiles = { block in getContentsOfDirectoryAtPath("/Users/kdj", block) }

listMyFiles { (result, error) in
    if let e = error {
        e.description
    }
    else if let filenames = result {
        filenames                     // [".bashrc", ... ]
    }
}

OK. Did not work in a Playground but fine in a project.
Is there any info on PlayGround limitations?

doesn't compile at all in swift 3. 21 error...