Puzzle

Difficulty: Easy · Puzzle 3 of 6 · Topic: Parameterized Class Puzzles

A class is parameterized by depth. Predict statics for depth 8 vs depth 16.

Code

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class fifo_cfg #(int DEPTH = 8);
  static int instances = 0;
  function new();
    instances++;
  endfunction
endclass

initial begin
  fifo_cfg#(8)  a = new();
  fifo_cfg#(8)  b = new();
  fifo_cfg#(16) c = new();
  $display("d8=%0d d16=%0d", fifo_cfg#(8)::instances, fifo_cfg#(16)::instances);
end

Hint

Each unique parameter value forms a different specialization type.

Step-by-step solution

1) Two objects are created for specialization `fifo_cfg#(8)` => its static is 2.
2) One object is created for specialization `fifo_cfg#(16)` => its static is 1.
3) Statics are independent because specializations are distinct types.

Answer

Answer: Output is `d8=2 d16=1`.

Why candidates get it wrong

People sometimes assume all integer-parameter variants share one static namespace.

Interviewer follow-up

How would you create one truly global instance counter for all DEPTH values?

Related topics

• Back to Parameterized Class Puzzles

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