Re: general c++ question

[John W. Eaton]

On 29-Aug-2007, Shai Ayal wrote:

| The one thing I didn't like at first is the set_XXX method:
| Until this morning I though it would be best not to allow direct
| change of properties not through the normal set(h,name,val) functions.
| This ensures that properties are checked for errors, and while it does
| carry a performance hit over direct access, the graphics backend does
| not need to set many values. However, this morning I remembered that
| thery are some  properties which are "read-only" -- informative
| properties such as mouse position etc... The easiest way to implement
| read-only properties is not to add them into the XXX::set function,
| but to add them to the XXX::get function. This dictates that the
| backend will have direct access to setting the methods not through the
| set function.

OK, I wasn't thinking about these kinds of things, and the set_X
functions are not really necessary for the rest of the patch to work.
But maybe we should make some additional changes.

Currently we have (for example):

  void
  axes::axes_properties::set (const property_name& name,
                              const octave_value& val)
  {
    bool modified = true;

    if (name.compare ("parent"))
      set_parent (val);
    else if (name.compare ("children"))
      children = maybe_set_children (children, val);
    else if (name.compare ("__modified__"))
      {
        __modified__ = val.bool_value ();
        modified = false;
      }
    else if (name.compare ("position"))
      position = val;
    else if (name.compare ("title"))
      {
        graphics_handle h = ::reparent (val, "set", "title",
                                        __myhandle__, false);
        if (! error_state)
          {
            if (! xisnan (title))
              gh_manager::free (title);

            title = h;
          }
      }
    ...

and this ensures some consistency, handles the special cases in which
setting some properties implies changes to other properties, etc.

Maybe we should rewrite this as simply

  void
  axes::axes_properties::set (const property_name& name,
                              const octave_value& val)
  {
    bool modified = true;

    ...
    else if (name.compare ("position"))
      set_position (val);
    else if (name.compare ("title"))
      set_title (val);
    ...

and have the individial set_X functions take care of handling the
dependent properties and consistency checks?

There may still be some special cases (I think at least the
__modified__ property).

jwe