Encapsulation

What is Encapsulation? #

Encapsulation is an object-oriented programming concept where internal class details (properties and methods) are hidden from outside access. It promotes data protection, modularity, and controlled access to sensitive parts of a class.

Access Control in SystemVerilog Classes #

In SystemVerilog, class properties are public by default — meaning they can be accessed directly using the dot (.) operator from outside the class.

To restrict access, SystemVerilog provides two access modifiers:

Access Control Summary

1.Public : Members are accessible from outside (default in SystemVerilog).

class Packet;
  int id;             // Can be accessed from outside
 function void display();
  $display("ID = %0d", id);
 endfunction
endclass

module tb;
 initial begin
  Packet pkt = new();
  pkt.id = 5;         // Accessing public variable
  pkt.display();  
 end
endmodule

2.Protected : Members are accessible in the class and its subclasses only.

class Base;
  protected int id = 42;
 function void display();
  $display("Base ID = %0d", id);
 endfunction
endclass

class Derived extends Base;
 function void show_id();
  $display("Derived accessing ID = %0d", id);   //Allowed
 endfunction
endclass

module tb;
 initial begin
  Derived d = new();
  d.show_id();       //Works
  // d.id = 10;      //Error: 'id' is protected 
 end
endmodule

3.Private: Class data members and methods are accessible only inside the class where it is defined and not accessible from outside the class or in derived classes.

class A;
  private int x = 42;
 function void show();
  $display("x = %0d", x);    //Allowed
 endfunction
endclass

class B extends A;
 function void try_access();
  $display("x = %0d", x);    //Error: private member not accessible
 endfunction
endclass