Interface Segregation
The ISP states that a class should not be forced to implement interfaces it does not use. Prefer many small, specific interfaces over one large general one.
PHP
Intermediate
5 min read
Interface Segregation Principle
Example
<?php
// Bad: one fat interface (ISP violation)
interface Worker {
public function work(): void;
public function eat(): void;
public function sleep(): void;
}
// Good: segregated interfaces
interface Workable { public function work(): void; }
interface Eatable { public function eat(): void; }
interface Sleepable { public function sleep(): void; }
class HumanWorker implements Workable, Eatable, Sleepable {
public function work(): void {}
public function eat(): void {}
public function sleep(): void {}
}
class Robot implements Workable {
public function work(): void {} // Robots do not eat or sleep
} Pro Tip
A good interface should have a cohesive set of related methods — if you need to write stub "not implemented" methods, the interface is too large.