API 设计准则

An API is to the programmer what a GUI is to the end-user. The 'P' in API stands for "Programmer", not "Program", to highlight the fact that APIs are used by programmers, who are humans.

We believe APIs should be minimal and complete, have clear and simple semantics, be intuitive, be easy to memorize, and lead to readable code.

• Be minimal: A minimal API is one that has as few public members per class and as few classes as possible. This makes it easier to understand, remember, debug, and change the API.
• Be complete: A complete API means the expected functionality should be there. This can conflict with keeping it minimal. Also, if a member function is in the wrong class, many potential users of the function won't find it.
• Have clear and simple semantics: As with other design work, you should apply the principle of least surprise. Make common tasks easy. Rare tasks should be possible but not the focus. Solve the specific problem; don't make the solution overly general when this is not needed.
• Be intuitive: As with anything else on a computer, an API should be intuitive. Different experience and background leads to different perceptions on what is intuitive and what isn't. An API is intuitive if a semi-experienced user gets away without reading the documentation, and if a programmer who doesn't know the API can understand code written using it.
• Be easy to memorize: To make the API easy to remember, choose a consistent and precise naming convention. Use recognizable patterns and concepts, and avoid abbreviations.
• Lead to readable code: Code is written once, but read (and debugged and changed) many times. Readable code may sometimes take longer to write, but saves time throughout the product's life cycle.

设计模式的六大原则

• 开闭原则（Open Close Principle）

  开闭原则的意思是：对扩展开放，对修改关闭。在程序需要进行拓展的时候，不能去修改原有的代码，实现一个热插拔的效果。简言之，是为了使程序的扩展性好，易于维护和升级。想要达到这样的效果，我们需要使用接口和抽象类，后面的具体设计中我们会提到这点。

• 里氏代换原则（Liskov Substitution Principle）

  里氏代换原则是面向对象设计的基本原则之一。 里氏代换原则中说，任何基类可以出现的地方，子类一定可以出现。LSP 是继承复用的基石，只有当派生类可以替换掉基类，且软件单位的功能不受到影响时，基类才能真正被复用，而派生类也能够在基类的基础上增加新的行为。里氏代换原则是对开闭原则的补充。实现开闭原则的关键步骤就是抽象化，而基类与子类的继承关系就是抽象化的具体实现，所以里氏代换原则是对实现抽象化的具体步骤的规范。

• 依赖倒转原则（Dependence Inversion Principle）

  这个原则是开闭原则的基础，具体内容：针对接口编程，依赖于抽象而不依赖于具体。

• 接口隔离原则（Interface Segregation Principle）

  这个原则的意思是：使用多个隔离的接口，比使用单个接口要好。它还有另外一个意思是：降低类之间的耦合度。由此可见，其实设计模式就是从大型软件架构出发、便于升级和维护的软件设计思想，它强调降低依赖，降低耦合。

• 迪米特法则，又称最少知道原则（Demeter Principle）

  最少知道原则是指：一个实体应当尽量少地与其他实体之间发生相互作用，使得系统功能模块相对独立。

• 合成复用原则（Composite Reuse Principle）

  合成复用原则是指：尽量使用合成/聚合的方式，而不是使用继承。

中间件：Redis