作者：Peng
今天我們讨論一下中介者模式(Mediator)。這次不從抽象定義開始，而是用現實世界中的一個場景來解釋它。在一個團隊裡，有産品經理，開發工程師，品質工程師。當開發完成了某些功能，将代碼送出到倉庫。相關環節人員，像品質工程師和産品經理需要被通知。
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protocol Collogue {
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var id: String { get }
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func send(message: String)
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func receive(message: String)
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}
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class Developer: Collogue {
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var id: String
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var qe: QE
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var pm: PM
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init(qe: QE, pm: PM) {
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self.id = "Developer"
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self.qe = qe
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self.pm = pm
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}
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func send(message: String) {
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qe.receive(message: message)
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pm.receive(message: message)
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}
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func receive(message: String) {
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print(message)
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}
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}
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class QE: Collogue {
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var id: String
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var developer: Developer
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var pm: PM
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init(developer: Developer, pm: PM) {
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self.id = "QE"
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self.developer = developer
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self.pm = pm
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}
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func send(message: String) {
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developer.receive(message: message)
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pm.receive(message: message)
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}
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func receive(message: String) {
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print(message)
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}
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}
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class PM: Collogue {
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var id: String
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var developer: Developer
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var qe: QE
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init(developer: Developer, qe: QE) {
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self.id = "PM"
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self.developer = developer
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self.qe = qe
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}
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func send(message: String) {
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developer.receive(message: message)
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qe.receive(message: message)
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}
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func receive(message: String) {
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print(message)
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}
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}
每個角色都需要持有另一個角色的執行個體，這種連接配接方式是高耦合的，且很不容易修改。
現在我們需要一個中介者幫助我們簡化這個系統。中介者的目的是幫助對象之間互相交流。它讓每個對象都是跟自己進行互動而不是其他對象。目前對象不需要持有别的對象，而是持有中介者。這樣将解耦系統，它的結構圖如下所示：
我們來寫一下代碼：
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protocol Mediator {
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func send(message: String, sender: Colleague)
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}
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class TeamMediator: Mediator {
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var colleagues: [Colleague] = []
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func register(colleague: Colleague) {
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colleagues.append(colleague)
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}
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func send(message: String, sender: Colleague) {
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for colleague in colleagues {
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if colleague.id != sender.id {
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colleague.receive(message: message)
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}
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}
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}
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}
通過持有中介者，那幾個角色對象變成了這樣：
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protocol Colleague {
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var id: String { get }
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var mediator: Mediator { get }
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func send(message: String)
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func receive(message: String)
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}
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class Developer: Colleague {
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var id: String
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var mediator: Mediator
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init(mediator: Mediator) {
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self.id = "Developer"
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self.mediator = mediator
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}
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func send(message: String) {
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mediator.send(message: message, sender: self)
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}
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func receive(message: String) {
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print("Developer received: " + message)
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}
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}
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class QE: Colleague {
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var id: String
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var mediator: Mediator
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init(mediator: Mediator) {
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self.id = "QE"
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self.mediator = mediator
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}
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func send(message: String) {
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mediator.send(message: message, sender: self)
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}
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func receive(message: String) {
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print("QE received: " + message)
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}
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}
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class PM: Colleague {
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var id: String
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var mediator: Mediator
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init(mediator: Mediator) {
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self.id = "PM"
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self.mediator = mediator
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}
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func send(message: String) {
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mediator.send(message: message, sender: self)
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}
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func receive(message: String) {
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print("PM received: " + message)
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}
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}
這樣一來，整個結構就變成了下面這樣：
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//usage
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let mediator = TeamMediator()
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let qe = QE(mediator: mediator)
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let developer = Developer(mediator: mediator)
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let pm = PM(mediator: mediator)
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mediator.register(colleague: developer)
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mediator.register(colleague: qe)
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mediator.register(colleague: pm)
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mediator.send(message: "Hello world!", sender: developer)