How to handle the properties in derived class

SystemVerilog
, ,
1

Deal All,

I’m trying to understand virtual function functionality with a simple example.


// Code your testbench here
// or browse Examples
 class Base;

   int   a =10;

  virtual function void method1();
    $display("Base: Method1");   
    method2();
  endfunction 

  virtual function void method2();
    $display("Base: Method2"); 

  endfunction

   virtual function void method3();
    $display("Base: Method3");   
   method2();
  endfunction 

endclass


class Derived extends Base;

  int   b=11;
  
  function void method1();
    $display("Derived: Method1");   
    method2();
  endfunction 

  function void method2();
    $display("Derived: Method2"); 

  endfunction

  function void method3();
    $display("Derived: Method3");   
   method2();
  endfunction

endclass

class Derived_two extends Derived;

  int   c=12;
  
   function void method1();
    $display("Derived_two: Method1");   
    method2();
  endfunction 

  function void method2();
    $display("Derived_two: Method2"); 

  endfunction

  function void method3();
    $display("Derived_two: Method3");   
   method2();
  endfunction

endclass

module test;

initial
begin

  Base base;
  Derived derived;
  Derived_two derived_two;
  
  derived_two = new();
  
  
  base = derived_two; 

  $display("Test2 ");
  base.method1();
  $display("----");
  base.method2();
  $display("----");
  base.method3();
  
  $display("Test3 ");
  $display(base.a);
  $display("----");
  $display(base.b);
  $display("----");
  $display(base.c);
 
  
end


endmodule

From above example , I learn that base can control the sub-classes by up-casting. this is very handy by up-casting.
But. I’ve got 2 question about properties and down-casting.

  1. Even I declared methods as virtual, I can’t access another properties except declared class
  $display(base.b);
                |
: *E,NOTCLM (testbench.sv,91|16): b is not a class item.
  $display(base.c);
                |
: *E,NOTCLM (testbench.sv,93|16): c is not a class item.

So I’m wondering that How do we access properties within virtual and Up-Casting topology?

  1. Why do we do Down-casting?