CODEWITHSUNDEEP
system-verilog
al01
al01

Reputation: 51

Hierarchical name component lookup failed

I'm trying to studying the case by referring https://verificationacademy.com/courses/systemverilog-oop-for-uvm-verification

To understand $cast, I've implemented as the below.

class A;
    int v=1;
endclass

class F extends A;
    int w=2;
endclass

class B extends A;
    int x=3;
endclass

class G extends B;
    int y=4;
endclass

class C extends B;
    int z=5;
endclass        

module test;
initial begin
    A a_h = new();
    B b_h;
    G g_h;
    C c_h;
    F f_h;
    $display(a_h.v);
    if ( $cast(c_h, a_h) )
        $display(c_h.z);
    else if ( $cast(g_h, a_h) )
        $display(g_h.y);
end
endmodule

But I've got just only

'1'

I think the below code doesn't work.

 if ( $cast(c_h, a_h) )
        $display(c_h.z);
    else if ( $cast(g_h, a_h) )
        $display(g_h.y);

Why does it have a Hierarchical name component lookup failed error?

If I want to cast G to A class then what am I supposed to do?

casting picture

I've got error message when I implemented like the below

module test;

B b_h = new();
G g_h = new();
C c_h = new();
F f_h = new();
A a_h = new();

initial begin

$cast(c_h, a_h);
$display(c_h.z);
$display(b_h.x);
$display(a_h.v);

The error messages

    $cast(c_h, a_h);
            |
ncsim: *E,BCLCST (./test1.sv,33|5): Invalid cast: a value with the class datatype '$unit_0x118af7fb::A' cannot be assigned to a class variable with the datatype '$unit_0x118af7fb::C'.
          5
          3
          1

As you can see, I've got 5, 3, 1 values but also Error message. Would you please let me know why I get this error message?

Upvotes: 0

Views: 7189

Answers (1)

Serge
Serge

Reputation: 12384

In order to do this cast, you have to allocate the derived class first, then use it as the base class and only then you can cast, as in the following example.

class A;
  int a = 1;
endclass
class B extends A;
  int b = 2;
endclass

module C;
  B b_h = new(); // << allocate the derived class
  B bb_h;
  A ba_h;

  initial begin
    ba_h = b_h;  // << assign derived class to the base

    if ($cast(bb_h, ba_h)) // << now you can cast base to another variable of class B (or to one of its bases).
      $display(bb_h.b);
  end
endmodule

Upvotes: 0

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