How is the method of Class M being executed without creating its object in Class A as shown in below code?

SystemVerilog
1 
class Class_M;
    mailbox mbm;
task run_m ;
         $display("Hey I'm class_M");
endtask 

function new(mailbox mbm);
     this.mbm=mbm;
endfunction
endclass : Class_M

class Class_A;
   mailbox mbd;
  Class_M m1;
  
function new(input mailbox mbm,input bit is_active_or_passive);
    if(is_active_or_passive == 1)begin
      $display("Is_active_or_passive == 1");
      m1=new(mbm);
    end
    $display("is_active_or_passive=%b",is_active_or_passive);
endfunction
  
task run_a;
     fork
       m1.run_m();
    join
endtask
endclass : Class_A

module ma;
 Class_A ah;
 mailbox mbm;
 initial begin
   mbm = new;
   ah = new(.mbm(mbm),.is_active_or_passive(1'b0));
   $display("AH=%p",ah);
   ah.run_a();
 end 

endmodule
2

In reply to J@ini:

The short answer is that, when Class_A is created (i.e. a new(…) is called for Class_A, it has a call to new() of m1 (which is new() of Class_M). Calling a new in Class_A, ensures a new call in Class_M.

If you remove the new to Class_M inside the new of Class_A, it will still compile, but you will see a Null pointer deference during run-time, as there is no memory allocated for the instance of Class_M.

Simpler example below::


class B;
  int b = 1;
endclass

class A;
  int a = 0;
  B B_i;
  
  function new();
    B_i = new();  //commenting this line will be a runtime error.
  endfunction
  
endclass


module test();
  A A_i;
  
  initial begin
    A_i = new();
    $display("Value of b in B is %0d",A_i.B_i.b); 
  end

  
endmodule
3

In reply to J@ini:

See Why is my code not failing when accessing non static method from not static class? | Verification Academy