swift - The Chain Responsibility pattern

概述The chain of responsibility pattern is useful when there are multiple objects that could take responsibility for a request but you don’t want to expose details of those objects to the calling componen

The chain of responsibility pattern is useful when there are multiple objects that Could take responsibility for a request but you don’t want to expose details of those objects to the calling component.

责任链模式:把两种/多种解决方案封装到到一个链里，提供一个封闭的接口一一尝试。

clIEnt:

let messages = [

Message(from:"bob@example.com",to:"joe@example.com",

subject:"Free for lunch?"),

Message(from:"joe@example.com",to:"alice@acme.com",

subject:"New Contracts"),19)"> Message(from:"pete@example.com",to:"all@example.com",

subject: "Priority: All-Hands Meeting"),

];

iflet chain =Transmitter.createChain(true) {

for msgin messages {

let handled = chain.sendMessage(msg);

println("Message sent:\(handled)");

}

}

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//1

struct Message {

let from:String;

let to:String;

let subject:String;

}

//2

class Transmitter {

var nextlink:Transmitter?;

required init() {}

func sendMessage(message:Message,handled:Bool =false) ->Bool {

if (nextlink !=nil) {

returnnextlink!.sendMessage(message,handled: handled);

}elseif (!handled) {

println("End of chain reached. Message not sent");

}

return handled;

}

classfunc createChain(localOnly:Bool) ->Transmitter? {

let transmitterClasses:[Transmitter.Type]

= localOnly ? [PriorityTransmitter.self,LocalTransmitter.self]

: [PriorityTransmitter.self,LocalTransmitter.self,RemoteTransmitter.self];

var link:Transmitter?;

for tClassin transmitterClasses.reverse() {

let existinglink = link;

link = tClass();

link?.nextlink = existinglink;

}

return link;

}

privateclassfunc matchEmailSuffix(message:Message) ->Bool {

iflet index =find(message.from,"@") {

return message.to.hasSuffix(message.from[Range<String.Index>(start:

index,end: message.from.endindex)]);

}

return false;

}

}

class LocalTransmitter :Transmitter {

overrIDefunc sendMessage(message:Message,var handled:Bool) ->Bool {

if (!handled &&Transmitter.matchEmailSuffix(message)) {

println("Message to\(message.to) sent locally");

handled =true;

}

returnsuper.sendMessage(message,handled: handled);

}

}

class RemoteTransmitter :Transmitter {

overrIDefunc sendMessage(message:Message,var handled:Bool) ->Bool {

if (!handled && !Transmitter.matchEmailSuffix(message)) {

println("Message to\(message.to) sent remotely");

handled =true;

}

returnsuper.sendMessage(message,handled: handled);

}

}

class PriorityTransmitter :Transmitter {

var totalMessages =0;

var handledMessages =0;

overrIDefunc sendMessage(message:Message,var handled:Bool) ->Bool {

totalMessages++;

if (!handled && message.subject.hasPrefix("Priority")) {

handledMessages++;

println("Message to\(message.to) sent as priority");

println("Stats: Handled\(handledMessages) of\(totalMessages)");

handled =true;

}

returnsuper.sendMessage(message,handled: handled);

}

}

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