VLSI DV Interview Puzzles · All levels

Template Method with Non-Virtual Wrapper

Predict output when non-virtual wrapper calls a virtual hook.

Puzzle

Difficulty: Easy · Puzzle 5 of 6 · Topic: Virtual Method Puzzles

Predict output when non-virtual wrapper calls a virtual hook.

Code

systemverilog

class base_seq;
  function void run();
    $display("base run pre");
    body();
    $display("base run post");
  endfunction
  virtual function void body();
    $display("base body");
  endfunction
endclass

class ext_seq extends base_seq;
  function void body();
    $display("ext body");
  endfunction
endclass

initial begin
  base_seq s = new ext_seq();
  s.run();
end

Hint

Analyze dispatch at each call site separately.

Step-by-step solution

diagram

1) `run()` itself is non-virtual, so base wrapper always executes.
2) Inside wrapper, `body()` is virtual, so derived hook executes.
3) Output order: `base run pre`, `ext body`, `base run post`.

Answer

Answer: Base wrapper runs, but virtual hook dispatches to derived body.

Why candidates get it wrong

People often assume non-virtual wrapper blocks all polymorphism inside it.

Interviewer follow-up

Where is this pattern used in UVM phases and callbacks?

Navigate