//---------------------------------------------------------------------------------------------- //BUILDER - A CREATIONAL PATTERN // | INTENT // | | for a complex object // | | | separate its construction from representation // | | | same construction process // | | | | can create different representations // | APPLICABILITY ----------------------------------------------------------------------------- // | | algorithm for creating a complex object should be // | | | independent of the parts // | | | | that make up the object // | | | | how they're assembled // | | construction // | | | must allow different representations // | STRUCTURE // | | builder // | | | Director |o------------>| Builder | // | | |-----------------------------| |-----------| // | | |Construct() | |BuildPart()| // | | | for all objects in structure| ^ // | | | builder.BuildPart() | | // | | |ConcreteBuilder|- - - - ->|Product| // | | |---------------| // | | |BuildPart() | // | | |GetResult() | // | PARTICIPANTS // | | Builder // | | | abstract interface // | | | | for creating product parts // | | ConcreteBuilder // | | | constructs and assembles product parts // | | | | by implementing the builder interface // | | | defines and keeps track of the representation it creates // | | | provides an interface for retrieving the product // | | Director // | | | constructs an object // | | | | using the builder interface // | | Product // | | | represents the complex object under construction // | | | | ConcreteBuilder // | | | | | builds the product's internal representation // | | | | | defines the process by which it's assembled // | | | includes // | | | | classes that define the constituent parts // | | | | interfaces for assembling the parts into the final result // | COLLABORATIONS ---------------------------------------------------------------------------- // | | Client // | | | creates the Director object // | | | configures it with the desired Builder object // | | Director // | | | notifies the builder whenever a part of the product should be built // | | Builder // | | | handles requests from the director // | | | adds parts to the product // | | Client // | | | retrieves the product from the builder // | | // | | aClient aDirector aConcreteBuilder // | | | | | // | | | |new ConcreteBuilder | // | | | |- - - - - - - - - - - - - - - - - - -|- - - - - - - - - - >| | // | | | | | | // | | | |new Director(aConcreteBuilder) | | // | | | |- - - - - - - - - - - - - - - - - ->| | | // | | | | | | | // | | | | | | // | | | |Construct() | | // | | | |----------------------------------->| |BuildPartA() | // | | | | | |------------------->| | // | | | | | | | | // | | | | | | | // | | | | | |BuildPartB() | // | | | | | |------------------->| | // | | | | | | | | // | | | | | | | // | | | | | |BuildPartC() | // | | | | | |------------------->| | // | | | | | | | | // | | | | | | // | | | |GetResult() | | // | | | |-------------------------------------|-------------------->| | // | | | | | | | // | | | | | // | | // | CONSEQUENCES // | | It lets you vary product's internal representation // | | | define a new kind of builder // | | Isolates code for construction and representation // | | | ConcreteBuilder // | | | | contains all the code // | | | | | to create and assemble a product // | | | code is written once // | | | | Directors can reuse it // | | | | | same set of parts to build Product variants // | | Finer control over the construction // | | | step by step // | | | | construction of the product under the director's control // | | | finished product // | | | | retrieved by the director from the builder // | IMPLEMENTATION ---------------------------------------------------------------------------- // | | Operation for each component defined by Builder // | | | does nothing by default // | | Assembly and construction interface // | | | step-by-step fashion // | | | general interface for all kinds of concrete builders // | | | | a model where // | | | | | construction results are appended to the product // | | | | | | is usually sufficient // | | | | if parts constructed earlier must be accessed // | | | | | director receives child nodes from the builder // | | | | | | passes them back to the builder to build the parent nodes // | | No abstract class for products // | | | products differ greatly // | | | client is in a position to know // | | | | concrete subclass of Builder in use // | | | | can handle its products accordingly // | | Empty methods as default in Builder // | | | clients override operations they're interested in // | CODE -------------------------------------------------------------------------------------- #include <SRC\Patterns\Patterns.mqh> namespace Builder { class Product { public: void Add(string); void Show(); protected: SAList parts; }; void Product::Add(string part) {parts+=part;} void Product::Show(void) {int c=parts.Count(); for(int i=0; i<c; i++) Print(parts[i]);} //---------------------------------------------------------------------------------------------- interface Builder { void BuildPartA(); void BuildPartB(); void BuildPartC(); Product* GetResult(); }; //---------------------------------------------------------------------------------------------- class Director { public: void Construct(); Director(Builder*); ~Director(); protected: Builder* builder; }; void Director::Director(Builder *b) {builder=b;} void Director::~Director(void) {delete builder;} void Director::Construct(void) { builder.BuildPartA(); builder.BuildPartB(); builder.BuildPartC(); } //---------------------------------------------------------------------------------------------- class ConcreteBuilder:public Builder { public: void BuildPartA(); void BuildPartB(); void BuildPartC(); Product* GetResult(); protected: Product product; }; //--- void ConcreteBuilder::BuildPartA(void) {product.Add("Part A");} void ConcreteBuilder::BuildPartB(void) {product.Add("Part B");} void ConcreteBuilder::BuildPartC(void) {product.Add("Part C");} Product* ConcreteBuilder::GetResult(void) {return &product;} //---------------------------------------------------------------------------------------------- class Client:public ClientExample {public: string Output(); void Run();}; string Client::Output() {return __FUNCTION__;} void Client::Run() { Builder* builder=new ConcreteBuilder; Director director(builder); director.Construct(); Product* product=builder.GetResult(); product.Show(); } } //OUTPUT --------------------------------------------------------------------------------------- // | Creational::Builder::Client::Output // | Part A // | Part B // | Part C
