In object-oriented PHP, what kinds of inheritance and reuse mechanisms are supported, and how are they typically achieved?

Introduction / Context:
Object-oriented PHP supports inheritance and other code reuse mechanisms that allow developers to build flexible, maintainable architectures. Understanding the limits and capabilities of inheritance in PHP is important for designing class hierarchies, implementing interfaces, and composing behaviour. Interviewers often ask about the types of inheritance PHP supports to see whether you know how to use extends, implements, and traits correctly.

Given Data / Assumptions:

• We are using PHP 5 or later with full support for classes, interfaces, and traits.
• We want to share behaviour and contracts between classes using inheritance like constructs.
• PHP does not provide multiple inheritance of concrete classes in the same way as some other languages.
• The question focuses on what is actually supported and how it is achieved.

Concept / Approach:
PHP supports single inheritance of classes, meaning a class can extend exactly one parent class using the extends keyword. This provides classic inheritance, where the child class inherits properties and methods of the parent. PHP also supports multiple interfaces via the implements keyword, allowing a class to commit to multiple contracts without inheriting implementation. Additionally, PHP introduces traits, which let you reuse method implementations across unrelated classes without forming a strict parent child hierarchy. Together, these features provide flexible reuse without the complexity of multiple class inheritance.

Step-by-Step Solution:
Step 1: Recall that a PHP class declares inheritance as class Child extends Parent, meaning Child inherits from exactly one Parent class. Step 2: Understand that attempting to extend multiple classes directly, such as extends Parent1, Parent2, is not allowed and will cause a parse error. Step 3: Recognize that classes can implement multiple interfaces: class MyClass implements InterfaceA, InterfaceB, InterfaceC. Step 4: Learn that traits are declared with the trait keyword and included in a class using the use keyword, allowing method reuse across classes without forming new inheritance chains. Step 5: Conclude that PHP supports single class inheritance combined with multiple interfaces and traits as its main inheritance and reuse mechanisms.

Verification / Alternative check:
You can verify these rules by writing small PHP test classes. Extending more than one class will cause a syntax error, confirming that multiple class inheritance is not supported. However, implementing multiple interfaces compiles successfully, and using multiple traits in a single class also works. The PHP manual explicitly describes PHP as a single inheritance language with support for interfaces and traits for additional flexibility, confirming this understanding.

Why Other Options Are Wrong:
Option B is incorrect because PHP does not provide a multi_extends keyword and does not allow multiple inheritance of classes. Option C is wrong because PHP clearly supports classes, interfaces, traits, and standard object oriented features. Option D is incorrect because PHP allows user-defined classes to extend other user-defined classes as well as some built in classes, not just built in ones.

Common Pitfalls:
A common pitfall is trying to simulate multiple inheritance by creating deep, complex hierarchies, which can lead to fragile designs. Another mistake is overusing traits for everything, which can make code harder to follow if traits are scattered across the project. Good practice is to use single inheritance for "is a" relationships, interfaces to define contracts, and traits for small, reusable behaviour chunks, keeping class design clear and maintainable.

Final Answer:
PHP supports single class inheritance via extends, plus additional reuse through multiple interfaces and traits, but it does not support multiple inheritance of concrete classes.