What are the types of inheritance in PHP?

In PHP, there are three types of inheritance:

1. Single inheritance: Single inheritance refers to the concept of a class inheriting properties and methods from a single parent class. In PHP, a class can extend only one parent class using the `extends` keyword. The derived class, also known as the child class, inherits all the public and protected properties and methods of the parent class.

   <?php
   
   class ParentClass {
       // properties and methods
   }
   
   class ChildClass extends ParentClass {
       // properties and methods
   }

2. Multiple inheritance (achieved through interfaces): Multiple inheritance refers to the concept of a class inheriting properties and methods from multiple parent classes. However, PHP does not support multiple inheritance directly between classes. Instead, PHP supports multiple inheritance through interfaces. An interface defines a contract that a class must adhere to by implementing its methods.

   <?php
   
   interface Interface1 {
       // methods
   }
   
   interface Interface2 {
       // methods
   }
   
   class ChildClass implements Interface1, Interface2 {
       // properties and methods
   }

   By implementing multiple interfaces, a class can inherit and implement the methods defined in those interfaces. This allows for achieving a form of multiple inheritance in PHP.
   It's important to note that PHP supports only single class inheritance but allows implementing multiple interfaces, providing a way to achieve similar functionality to multiple inheritance.

3. Multi-level inheritance: Multi-level inheritance refers to the concept of a class inheriting properties and methods from a parent class, which itself has inherited from another parent class. In this type of inheritance, a class extends a class that has already extended another class.

   <?php
   
   class GrandParentClass {
       // properties and methods
   }
   
   class ParentClass extends GrandParentClass {
       // properties and methods
   }
   
   class ChildClass extends ParentClass {
       // properties and methods
   }
   

   In the above example, the ChildClass inherits properties and methods from both the ParentClass and the GrandParentClass. It forms a chain where the ChildClass indirectly inherits the properties and methods from the GrandParentClass through the ParentClass.

   Multi-level inheritance allows classes to inherit and extend the functionality of multiple classes in a hierarchical manner. The child class can access the properties and methods of both its immediate parent class and its ancestor classes.

   In PHP, a class can directly extend only one parent class. However, through multi-level inheritance, a class can indirectly inherit from multiple classes similar to multiple inheritance through interfaces.