Summary of design pattern

Assemble design pattern

每种design pattern都提出了一种核心思想/抽象思路，现实问题往往非常复杂，仅仅依靠一种design pattern是难以描述的，因此就需要assemble多种 design pattern来描述复杂的现实问题。

Node is like event/message

在visitor pattern中，需要traverse node in the structure，对于不同type的node，需要执行不同的algorithm，其实这非常类似于与event/message driven model的，即对于不同type的event/message，执行不同的callback；

Example

1、Active-object+observer+visitor

参见工程parallel-computing的Concurrent-computing\TODO-Concurrent-server\Design-pattern\Active-object+observer+visitor章节

Abstraction

本节从Abstraction的角度来分析各种design pattern:

1、command是对各种operation的更加abstract的描述；

2、iterator是对各种container的更加abstract的描述；

Structure

本节从structure的角度来分析各种design pattern;

1、composit pattern: tree

2、chain of responsibility pattern: chain

3、decorator pattern: chain

Command pattern VS visitor pattern

command 和 visitor都对应的是operation/algorithm。

关于此，在 refactoring.guru Visitor 中有这样的描述:

You can treat Visitor as a powerful version of the Command pattern. Its objects can execute operations over various objects of different classes.

decorator pattern VS

TODO

stackoverflow visitor vs servant vs command patterns

Chain of responsibility VS decorator pattern

这两种pattern是非常值得对比的，在下面的文章中对它们进行了对比:

a、wikipedia Decorator pattern

b、refactoring.guru Chain of Responsibility

Dynamic pipeline flow of handling request

两种pattern都能够Pipeline flow of handling request。

Message/event/request processing pattern/flow of request

pipeline flow of request

refactoring.guru Chain of Responsibility、

Chain of Responsibility, Command, Mediator and Observer address various ways of connecting senders and receivers of requests:

1、Chain of Responsibility passes a request sequentially along a dynamic chain of potential receivers until one of them handles it.

2、Command establishes unidirectional connections between senders and receivers.

3、Mediator eliminates(消除) direct connections between senders and receivers, forcing them to communicate indirectly via a mediator object.

4、Observer lets receivers dynamically subscribe to and unsubscribe from receiving requests.

refactoring.guru Command

AOP

对于 "flow of handling request" 即流程相关的，也非常适合用AOP来进行抽象。

Interface: Adapter、Decorator、Facade

这三种idiom都是围着interface转，在各自的Wikipedia page中，都对它们进行了对比，总结得不错:

Pattern	Intent
Adapter	Converts one interface to another so that it matches what the client is expecting
Decorator	Dynamically adds responsibility to the interface by wrapping the original code
Facade	Provides a simplified interface