Casting a class multiple levels - possible?

SystemVerilog
, ,
1

Say I have these classes:

class base;
int x;
endclass

class derive1 extends base;
int y;
endclass

class derive2 extends derive1;
int z;
endclass

Is it possible to cast a base class instance straight to a derive2 class instance? like this:

program prg;
base b1;
derive2 d2;

$cast(d2,b1);

endprogram

2

Certainly. But it will only work if the object is being cast is indeed a derive2 class.
Here is a complete self-contained example, with code tags. Please show your code this way so it is easy for others to give it a try.

module prg;
class base;
  int x;
endclass

class derive1 extends base;
  int y;
endclass

class derive2 extends derive1;
  int z;
endclass
base b1,b;
derive2 d2,d;
initial begin
   d = new();
   b1 = d; // no $cast needed
   $cast(d2,b1); // $cast needed, and will succeed
   b1 = new;
   $cast(d2,b1); // $cast needed, and will fail
  end
endmodule
3

In reply to dave_59:

why $cast will fail when child handler d2 pointing parent b1

4

In reply to ramana4210:

I would avoid using the terms parent and child when discussing inheritance. A derived class object includes (inherits) all properties of the base class type - it is not a separate object.

The reason the last $cast fails is that b1 holds a handle to a base type class object. It has no proprieties that the target class variable needs. i.e. d2.z does not exist.