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Visitor Pattern in TypeScript
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| interface Visitor<TElementTypes = any> { | |
| visit(element: TElementTypes): void; | |
| } | |
| interface ConcreteItem { | |
| accept(visitor: Visitor): void; | |
| } | |
| class ConcreteItemA implements ConcreteItem { | |
| accept(visitor: Visitor): void { | |
| visitor.visit(this); | |
| } | |
| } | |
| class ConcreteItemB implements ConcreteItem { | |
| accept(visitor: Visitor): void { | |
| visitor.visit(this); | |
| } | |
| } | |
| type ConcreteItems = ( | |
| | ConcreteItemA | |
| | ConcreteItemB | |
| ); | |
| class ConcreteVisitor implements Visitor<ConcreteItems> { | |
| visit(item: ConcreteItems): void { | |
| switch (item.constructor) { | |
| case ConcreteItemA: | |
| return this.visitA(item); | |
| case ConcreteItemB: | |
| return this.visitB(item); | |
| } | |
| } | |
| private visitA(item: ConcreteItemA): void { | |
| return console.log('Visiting A...'); | |
| } | |
| private visitB(item: ConcreteItemB): void { | |
| return console.log('Visiting B...'); | |
| } | |
| } | |
| console.clear(); | |
| const a = new ConcreteItemA(); | |
| const b = new ConcreteItemB(); | |
| const visitor = new ConcreteVisitor(); | |
| visitor.visit(a); | |
| visitor.visit(a); | |
| visitor.visit(b); | |
| visitor.visit(a); | |
| visitor.visit(b); |
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