Re: FYI: subasgn argument optimization

[Jaroslav Hajek]

On Fri, Aug 14, 2009 at 5:39 PM, John W. Eaton<address@hidden> wrote:
> On 13-Aug-2009, Jaroslav Hajek wrote:
>
> | PS. This patch rebases octave_class on top of octave_struct.
>
> It seems that would be a good thing.  I can no longer remember why
> I didn't do it originally.  I don't think I would have avoided
> inheritance unless I had a reason, but then maybe I didn't realize how
> similar classes were to structs.
>

Maybe you had a reason; anyway, my implementation spanned a lot more
problems with inheritance than it was worth, so I reverted the
rebasing:
http://hg.savannah.gnu.org/hgweb/octave/rev/8e5009334661
and I just injected code from ov-struct.cc to optimize out a useless
copy on nested assignment on fields:
obj.x(1) = 1; // does copy x in 3.2.x if x is an object.

Of course, the injection is what I wanted to avoid by using
inheritance, but right now I think it should be done without altering
octave_struct or not done at all.
Your implementation handles multidimensional objects, or inheritance,
but not both (actually, even constructing such things fails):

@foo/foo.m
function f = foo ()
  a = struct ("x", {1 2 3 4});
  f = class (a, "foo");
end

@bar/bar.m
function b = bar ()
  a = struct ("y", {1 2 3 4});
  b = class (a, "bar", foo());
end

octave:1> a = foo
octave:2> b = bar
error: invalid structure assignment
error: called from:
error:   /home/hajek/devel/octave/patches/@bar/bar.m at line 3, column 5

the basic problem is (besides missing code support in the nested part
of octave_class::subsasgn) that you can't store a single object inside
a field of multidimensional Octave_map - all fields must be the same
size.

Maybe a possible solution would be to not store parent objects as
regular fields, but separately; you'd need to hack the field lookup
for that and probably also plain () indexing and indexed assignment.
But then I still wonder what obj.parent_class_name is supposed to do
if obj is multidimensional (normally, you should get a cs-list).
Apparently the old OOP model is documented only poorly from Matlab,
and I don't have Matlab, so I should probably resist further playing
with this part to avoid breaking something.

-- 
RNDr. Jaroslav Hajek
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz