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clone() and copy() Methods: Code Examples

Code Examples for clone() and copy() Methods.

Code examples

Base class copy/clone contract

systemverilog
class txn_base;
  rand bit [31:0] addr;
  rand bit write;

  virtual function void copy(txn_base rhs);
    addr = rhs.addr;
    write = rhs.write;
  endfunction

  virtual function txn_base clone();
    txn_base c = new;
    c.copy(this);
    return c;
  endfunction
endclass

copy moves state between already-allocated objects. clone guarantees a fresh object by allocating first and then reusing copy logic.

Derived override with super.copy and $cast

systemverilog
class write_txn extends txn_base;
  rand bit [63:0] data;

  virtual function void copy(txn_base rhs);
    write_txn wrhs;
    super.copy(rhs);
    if (!$cast(wrhs, rhs)) begin
      return;
    end
    data = wrhs.data;
  endfunction

  virtual function txn_base clone();
    write_txn c = new;
    c.copy(this);
    return c;
  endfunction
endclass

The super.copy call guarantees base fields are handled once. The $cast protects derived field copy from type mismatch when the API accepts base handles.

Scoreboard stores clones for stable history

systemverilog
class scoreboard;
  txn_base exp_q[$];

  function void push_expected(txn_base tr);
    exp_q.push_back(tr.clone());
  endfunction
endclass

Queueing clones avoids later mutation of producer-owned handles and keeps expected history immutable from the scoreboard point of view.

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