> The following was supposedly scribed by
> darren chamberlain
> on Wednesday 21 January 2004 02:11 pm:
>* Eric Wilhelm <ewilhelm at sbcglobal.net> [2004/01/21 13:58]:
>> > The following was supposedly scribed by
>> > darren chamberlain
>> > on Wednesday 21 January 2004 11:10 am:
>
>"Supposedly"? Aren't you verifying signatures? ;)
:) no. That's just the quote line.
>Well, if polymorphism isn't what you're after, couldn't you have
>CAD::Drawing::IO not define a load function, and have
>CAD::Drawing::IO::Foo declare package CAD::Drawing::IO and define a
>load? Then, the user need simply do:
>
> use CAD::Drawing::IO;
> use CAD::Drawing::IO::OpenDWG;
>
>And calling load("file.dwg") uses the load defined in ::IO::OpenDWG?
But this still (essentially) leaves the user with hard-coded information about
which format to use (making it impossible to do $drw->save($ARGV[0])). My
goal is to make all of the file formats (smile floormats) transparent in the
hope that they eventually go away completely.
>Without any knowledge of the implementation, however, it sounds like
>what you want is polymorphism, and you're jumping through hoops to avoid
>using it.
What I'm going for is more like a big chain of elsif statements which is put
together out of multiple packages. If the user were to use an object from
CAD::Drawing::IO::OpenDWG to call the save() function, that would be
polymorphism. I might be jumping through hoops at the module level, but I
think this beats making the user jump through hoops at the main program
level.
>> With this model, your main program would not have "use
>> CAD::Drawing::IO::IGES;", but simply "use CAD::Drawing;".
>
>This sounds exactly like DBI, which relies on DBDs being polymorphic.
>*shrug*
It is a lot like the DBI::connect() function, but load() does not return an
object the way connect() does. With DBI, once it gets hold of a classed
object, DBI.pm is home-free and just has to return the blessed object,
leaving the rest up to the polymorphism.
My problem is more like DBI turned on its head. e.g. with DBI::connect() you
are at the beginning of the program and you get your $dbh which is used to
call $dbh->select*foo() and such.
With CAD::Drawing, you get your $drw from CAD::Drawing->new() and from there
you can either $drw->load("whatever.dwg|dxf") or just start adding entities
to the drawing. At the end (or the middle, or as many times as you like),
you can $drw->save("file.ps") && $drw->save("file.dxf") &&
$drw->save("file.png", {size => [640,480]}) && $drw->save("file.dwg.gz").
Now, if I could just get the string "file.ps" to kindly bless itself into
CAD::Drawing::IO::PostScript, I'd be in the free and clear;-)
Seriously, though. That is basically what I'm trying to do. Consider this,
where you have a list of available packages in @found, and a $filename with
(or without) an extension, and possibly an explicit $options{type} argument,
and the following is part of the IO::save() function:
foreach my $package (@found) {
if(eval("\$" . $package . "::can_save(\$filename, \$options{type})") ) {
my $r = eval($package . "::save_file(\$self, \$filename, \\%options)")
return($r);
}
}
Thanks,
Eric
--
A counterintuitive sansevieria trifasciata was once literalized guiltily.
--Product of Artificial Intelligence
