ch11-interface-segregation-principle.md

Interface Segregation Principle

Introduction

The Interface Segregation principle states that no implementation of an interface should be forced to depend on methods it does not use.

(接口隔离原则规定在实现接口的时候，不能强迫去实现没有用处的方法。)

this principle demands that interfaces be granular and focused.

(该原则要求接口必须粒度很细，且专注于一个领域。)

Instead of having a “fat” interface containing methods not needed by all implementations, it is preferable to have several smaller interfaces that may be implemented individually as needed.

In Action

interface SessionHandlerInterface {
    public function close();
    public function destroy($sessionId);
    public function gc($maxLifetime);
    public function open($savePath, $name);
    public function read($sesssionId);
    public function write($sessionId, $sessionData);
}

consider an implementation using Memcached. Would a Memcached implementation of this interface define functionality for each of these methods? Not only do we not need to implement all of these methods, we don't need half of them!

we do not need to implement the gc method of the interface, nor do we need to implement the open or close methods of the interface.

To correct this problem, let's start by defining a smaller, more focused interface for session garbage collection:

interface GarbageCollectorInterface {
    public function gc($maxLifetime);
}