Inheritance

What is Inheritance? #

Inheritance is a fundamental concept in Object-Oriented Programming (OOP), and SystemVerilog fully supports it through class-based modeling. In simple terms, inheritance allows a class (called the child class) to automatically acquire the properties and behaviors (variables and methods) of another class (called the parent class or base class).

This promotes:

• Code reuse (don’t repeat what already exists)
• Hierarchy-based modeling (natural representation of relationships)
• Modularity and extensibility (easy to expand or override behavior)

Syntax:

class Parent;
  // variables and methods
endclass

class Child extends Parent;
  // additional variables and methods
endclass

Example:

class Animal;
  function void speak();
    $display("Animal makes sound");
  endfunction
endclass

class Dog extends Animal;
  function void bark();
    $display("Dog barks");
  endfunction
endclass

// Usage
module test;
  initial begin
    Dog d = new();
    d.speak(); // Inherited from Animal
    d.bark();  // Defined in Dog
  end
endmodule

Output: Animal makes sound
        Dog barks

Dog inherits the speak() method from Animal, It can also define its own method like bark().

Overriding Parent Methods #

You can override a method in the child class using the same name.

class Animal;
  function void speak();
    $display("Animal speaks");
  endfunction
endclass

class Cat extends Animal;
  function void speak();
    $display("Cat meows");
  endfunction
endclass

// Usage
module test;
  initial begin
    Cat c = new();
    c.speak();   
  end
endmodule

Now, calling speak() from a Cat object will run the child version, not the parent version.

Output: Cat meows

The super Keyword #

If you still want to call the parent’s method that is overridden by the child class, use super.

class Animal;
  function void speak();
    $display("Animal speaks");
  endfunction
endclass

class Cat extends Animal;
  function void speak();
    super.speak();         // calling parent class method
    $display("Cat meows");
  endfunction
endclass

// Usage
module test;
  initial begin
    Cat c = new();
    c.speak();   
  end
endmodule

Output: Animal speaks
        Cat meows

Quick Summary #