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Behaviors.swift
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Behaviors.swift
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// MIT License
//
// Copyright (c) 2016 Kevin Randrup
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
import Swift
import Foundation
/// This is a working implementation of behaviors using the existing protocol system.
/// It very easy to learn and matches what you would expect from the existing Swift standard library.
/// To create a new Behavior all you need to do is implement the Behavior protocol.
protocol Behavior {
associatedtype Value
/// InitializationValue can be used to require a different value on initialization.
/// Ex. a closure which generates a default property or creates a database.
associatedtype InitializationValue = Value
init(_ initValue: InitializationValue)
mutating func get() -> Value
mutating func set(_ newValue: Value)
}
/// This extension gives the ability to initialize a behavior when the
/// InitializationValue can be created from nil (Eg. optional values).
/// `var myBehavior: BehaviorName<Type?> = BehaviorName()`
extension Behavior where InitializationValue : ExpressibleByNilLiteral {
init() {
self.init(nil)
}
}
// Once condititional conformances are added to Swift the following will hopefully be possible.
// https://github.com/apple/swift-evolution/blob/master/proposals/0143-conditional-conformances.md
// extension Behavior : ExpressibleByNilLiteral where InitializationValue : ExpressibleByNilLiteral {}
/// The Lazy Behavior has an initial value that it falls back onto.
/// Lazy properties can be cleared to restore the initial value
struct Lazy<LazyValue> : Behavior {
typealias Value = LazyValue
var value: Value?
let initialValue: Value
init(_ initValue: Value) {
initialValue = initValue
}
mutating func get() -> Value {
if let value = value {
return value
}
value = initialValue
return initialValue
}
mutating func set(_ newValue: Value) {
value = newValue
}
/// Lazy is just a struct so we can of course add our own methods.
mutating func clear() {
value = initialValue
}
}
var lazyInt = Lazy(5)
lazyInt.get() // 5
lazyInt.set(2)
lazyInt.get() // 2
lazyInt.clear()
lazyInt.get() // 5
/// DelayedImmutable properties can only be set once but they aren't required to be set during initialization.
/// If behaviors get built into the compiler, this behavior could be added to IBOutlets to avoid using ImplicitlyUnwrappedOptional
struct DelayedImmutable<DelayedValue> : Behavior {
typealias Value = DelayedValue
// Provide an InitializationValue to allow DelayedImmutable to be initialized with an Optional.
typealias InitializationValue = Value?
var value: Value?
init(_ initValue: InitializationValue) {
value = initValue
}
func get() -> Value {
guard let value = value else {
fatalError("property accessed before being initialized")
}
return value
}
mutating func set(_ newValue: Value) {
if value != nil {
fatalError("property initialized twice")
}
value = newValue
}
}
//Can initialize with nothing
var delayedImmutable: DelayedImmutable<Int> = DelayedImmutable()
//delayedImmutable.get() //Fatal error
delayedImmutable.set(1)
//delayedImmutable.set(2) //Also fatal error
/// Observer Behavior can notify others before or after a value is set
struct Observer<ObservedValue> : Behavior {
typealias Value = ObservedValue
var value: Value
init(_ initValue: Value) {
value = initValue
}
var willSet: ((_ newValue: Value) -> Void)?
var didSet: ((_ newValue: Value) -> Void)?
func get() -> Value {
return value
}
mutating func set(_ newValue: Value) {
willSet?(newValue)
value = newValue
didSet?(newValue)
}
}
var observedInt = Observer(5)
/// This closure is stored in the Observer Behavior.
/// If Observer is a class then the closure would need to
/// capture observedInt as [unowned observedInt] to avoid the retain cycle.
observedInt.willSet = { (newValue) -> Void in
let previous = observedInt.get()
print("Previous Value: \(previous)\nNew Value: \(newValue)")
}
observedInt.set(2) //Previous: 5, New: 2
observedInt.set(3) // Previous: 2, New: 3
/// Showcasing the Behavior initializer the behavior type is an Optional
var observedOptionalInt: Observer<Int?> = Observer()
/// Copying Behavior implements defensive copying.
/// This behavior implmented the `copy` attribute from Objective-C
struct Copying<CopyableValue : NSCopying> : Behavior {
typealias Value = CopyableValue
var value: Value
init(_ initValue: Value) {
value = initValue.copy() as! Value
}
func get() -> Value {
return value
}
mutating func set(_ newValue: Value) {
value = newValue.copy() as! Value
}
}
let oldArray: NSArray = NSMutableArray(arrayLiteral: 1, 2)
var array = Copying(oldArray)
(oldArray as! NSMutableArray).add(3)
print("Old array - [\(oldArray.componentsJoined(by: ", "))]") // [1, 2, 3]
print("New array - [\(array.get().componentsJoined(by: ", "))]") // [1, 2]