[Octave-bug-tracker] [bug #65200] Special nil octave_base_value class to speed up octave_value dtors

[John W. Eaton]

Follow-up Comment #6, bug#65200 (group octave):

In the nil_rep changeset, what is meant by the comment "// Also increased in
octave_base_value()"?  I don't see any change to the octave_base_value default
constructor.

How much does this really save?  Could we achieve the same thing (avoiding the
"m_rep != nil_rep ()" test in by modifying the nil_rep function to be


octave_base_value * octave_value::nil_rep ()
{
  static bool initialized = false;
  static octave_base_value nr;

  if (! initialized)
    {
      // Artificially increment count for NR so that it should never
      // reach zero and NR will never be a candidate for deletion.

      nr.m_count++;
      initialized = true;
    }

  return &nr;
}


If using a separate class is better, then why is it better?  If the reason is
performance, is it actually a measurable difference?

If we do decide use the class, I don't think the reinterpret_cast is needed,
or it wouldn't be if the full declaration of the octave_nil_value class were
available in ov.h and if it used public inheritance.  Is there some reason the
full declaration can't be available there and a reason to use private
inheritance?  Also, make the octave_value_nilrep object a static member of the
octave_nil_value class instead of a global variable.

We should also define or explicitly default or delete the common constructors,
operators, and destructor.  Finally, the grammar of the comment for the
octave_nil_value class should be fixed and it would be good if the commit
message also follows the project style guidelines.


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