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Is it a must to declare with keyword 'virtual' when define a task in a child class with the same name as its parent?

Jeff000

Look into the code as below, the task whoAmI() is not declared using 'virtual', but when calling it from class B, it actually get B's task executed. Then it seems that the 'virtual' keyword is not necessary here?

class A;

   task whoAmI();
      $display("This is A");
   endtask // whoAmI
  
endclass // A

class B extends A;

     task whoAmI();
        $display("This is B");
     endtask // whoAmI
endclass // B
  
B b = new();
b.whoAmI();

  • Without any "virtual" keyword, SV will call the function based on the type of handle used to invoke it. Since the handle "b" is of type "B", the class B version of the function will be called.

    The "virtual" keyword comes into play when you are using a base class handle to reference a derived class object (polymorphism).

    A a;
    B b = new();
    a = b;
    a.whoAmI();

    Without the virtual keyword, the call to a.shoAmI will return "This is A". With the virtual keyword, it will return "This is B".

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