How to use constraint_mode to shut off constraint in base_trans A, when I have A_ext type

SystemVerilog
,
1 
class A;
endclass

class B extends A;
    constraint c_B {};
endclass

class C extends B;
endclass

In test, I define A_tr with A type,
----A A_tr;
and override the type with C;
----set_type_override_by_type(A::get_type, C::get_type);

Now, I want to shut off constraint c_B, then I define B_tr with B type,
----B B_tr;
And then,
----B_tr = A_tr; //Since A_tr now is of type C; if i use $cast(B_tr, A_tr), the result is the same
----B_tr.c_B.constraint_mode(0);

When compile, it will report Error :
“The expression B_tr.c_B,constraint_mode contains a reference to constraint c_B, which is allowed only to to call the constraint_mode()”

2

In reply to sages:
You asked the same question 4 years ago. how to use constraint_mode to control one constraint in an override ovm_object | Verification Academy

3

In reply to dave_59:

Hi Dave,
Yes, I have this similar question 4 years ago, but seems different.

Actually, these two should be the same problem. Thus I tried define a trans B_tr and assign A_tr(now is type C) to handler B_tr, I think B_tr could access constraint c_B, and shut if off, but seems to fail. And error report now is “The expression B_tr.c_B,constraint_mode contains a reference to constraint c_B, which is allowed only to to call the constraint_mode()”.
So, I’m confused.

PS, the previous one reports Error “Could not find member c_B in class A_h”

4

*In reply to sages:*You need to show more code, particularly the context where the error occurs.