error.swift

// Playground - noun: a place where people can play

import Foundation

enum Result<ValueType, ErrorType> : LogicValue {
    case Value(ValueType)
    case Error(ErrorType)

    var successful : Bool {
        get {
            switch self {
                case .Value: return true
                case .Error: return false
            }
        }
    }

    var value : ValueType? {
        get {
            switch self {
                case .Value(let v): return v
                case .Error: return nil
            }
        }
    }

    var error : ErrorType? {
        get {
            switch self {
                case .Value: return nil
                case .Error(let e): return e
            }
        }
    }

    func getLogicValue() -> Bool {
        return self.successful
    }

}

// #############################################################################

// This example shows a function that just wants to return success or failure
func F1() -> Result<Void, String> {
    return .Value()
}

// This example shows a function that just returns a string value
func F2() -> Result<String, Int> {
    return .Value("This was a triumph")
}

// This example shows a function that fails with an error code
func F3() -> Result<String, Int> {
    return .Error(-666)
}

// If based handling
let result = F1()
if result {
    println(result.value)
} else {
    println(result.error)
}

// Switch based handling - have to handle all cases
switch F1() {
case .Value(let v):
    println(v)
case .Error(let e):
    println(e)
}