Being one of the big pillars of Object-Oriented Design, The Interface Segregation Principle (ISP) permits you to define fine-grained contracts that provide client classes with the functionality to perform a set of well-defined tasks. As with other SOLID principles (Single responsibility, Open-closed, Liskov substitution, Interface segregation and Dependency inversion), ISP is language-agnostic, meaning that it can be applied in several programming languages, including PHP.

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