try() for discriminated-union error handling in Swift

gistfile1.swift

import Foundation


// Because the real thing crashes
enum Result {
	case Value(Any)
	case Error(NSError?)
}


func try<T>(f: (NSErrorPointer) -> T?) -> Result {
	var error: NSError?
	let result = f(&error)
	if result {
		return .Value(result!)
	} else {
		return .Error(error)
	}
}


let fm = NSFileManager.defaultManager()
let x = try { fm.contentsOfDirectoryAtPath("/", error:$0) }

switch x {
	case .Value(let v):
		println("Success: \(v)")
	case .Error(let e):
		println("Error: \(e)")
}