visitor | 易学教程

Implementing the visitor pattern using C++ Templates

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问题 I've been trying to reduce the amount of boilerplate in my code, by using C++ Templates to implement the visitor pattern. So far I've come up with this: class BaseVisitor { public: virtual ~BaseVisitor() {} }; template<typename T> class Visitor : public BaseVisitor { public: virtual void visit(T& /* visitable */) = 0; }; template<typename Derived> class Visitable { public: void accept(Visitor<Derived>& visitor) { visitor.visit(static_cast<Derived&>(*this)); } }; And each subclass of Visitable

Visitor pattern's purpose with examples [duplicate]

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This question already has an answer here: When should I use the Visitor Design Pattern? [closed] 20 answers I'm really confused about the visitor pattern and its uses. I can't really seem to visualize the benefits of using this pattern or its purpose. If someone could explain with examples if possible that would be great. Once upon a time... class MusicLibrary { private Set<Music> collection ... public Set<Music> getPopMusic() { ... } public Set<Music> getRockMusic() { ... } public Set<Music> getElectronicaMusic() { ... } } Then you realize you'd like to be able to filter the library's

What is the point of accept() method in Visitor pattern?

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问题 There is a lot of talk on decoupling the algorithms from the classes. But, one thing stays aside not explained. They use visitor like this abstract class Expr { public <T> T accept(Visitor<T> visitor) {visitor.visit(this);} } class ExprVisitor extends Visitor{ public Integer visit(Num num) { return num.value; } public Integer visit(Sum sum) { return sum.getLeft().accept(this) + sum.getRight().accept(this); } public Integer visit(Prod prod) { return prod.getLeft().accept(this) * prod.getRight(

Visitor Pattern Explanation

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问题 So I've read up all the documentation about the Visitor pattern, and I'm still mightily confused. I've taken this example from another SO question, could someone help me understand? For instance when do we use a visitor design pattern? I think I may have understood some of it, but I'm just not able to see the bigger picture. How do I know when I can use it? class equipmentVisited { virtual void accept(equipmentVisitor* visitor) = 0; } class floppyDisk : public equipmentVisited { virtual void

Difference betwen Visitor pattern & Double Dispatch

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问题 I am reading about visitor pattern, and it appears the same like Double Dispatch. Is there any difference between the two. Do the two terms means the same thing. reference: http://www.vincehuston.org/dp/visitor.html 回答1: In short they come from to different conceptualizations that, in some languages where double dispatch is not natively supported, lead to the visitor pattern as a way to concatenate two (or more) single dispatch in order to have a multi-dispatch surrogate. In long The idea of