`randc` not legal with `solve`

Coverage
1

I cannot figure out why the following code works with rand but not randc.
I’d like to hit all posible states of a before they start repeating in randomization, that is why i want randc.

class myclass;
  rand var byte a,b;
   // randc var byte a,b;  <- does not work
  constraint spec0 {
    a inside {[1:5]};
    b inside {1,-1};
    a == 3 -> b == -1;
    solve a before b;
  }
endclass

module tb;  
  initial begin
    myclass abc = new();
    repeat(10) begin
      assert(abc.randomize());
      $display("[i] rand abc.a = %0d, abc.b = %0d",abc.a,abc.b);
  	end
  end
endmodule

Thank you for the help you can provide.

2

In case of randc, you need to remove solve.. before
2017 LRM : 18.5.10 Variable ordering “randc variables are not allowed. randc variables are always solved before any other.”

3

In the latest LRM (1800-2023), this is in section 18.5.9.

Also, your simulator should give you an error message explaining why you can’t use ‘solve…before…’ with randc variables.

4

As the others have replied, the LRM does not allow a randc variable with a solve before construct–randc enforces a implicit solving order.

It’s also nonsensical to have both a and b be cyclic random variables. Given the constraints you’ve imposed on them, it’s impossible for that to happen.