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Moin,
On Tuesday 24 February 2004 23:41, chromatic wrote:
> On Tue, 2004-02-24 at 11:02, John Beppu wrote:
> > The has() method in this release has a bug.
> >
> > Here's how it looks right now:
> >
> > sub has
> > {
> > my ($class, $define) = @_;
> > scalar grep { exists $$sdl_config{$_}{$define} } keys
> > %$sdl_config; }
> >
> > Unfortunately, even if certain attributes are set to 0,
> > the existence check still passes. For example, I don't
> > have SDL_ttf on my system, and the $sdl_config hashref
> > knows this. However,
> >
> > SDL::Config->has('SDL_ttf')
> >
> > returns 1;
> >
> > Get rid of "exists" and it'll work as advertised.
>
> True, but it'll eat up memory in the hash if you pass undefined
> subsystem names. That's why the original version was:
>
> sub has
> {
> my ($class, $define) = @_;
>
> while (my ($name, $subsystems) = each %$sdl_config)
> {
> next unless exists $subsystems->{ $define };
> return $subsystems->{ $define } ? 1 : 0;
> }
>
> return;
> }
>
> Maybe it was silly to optimize this never to use any more memory or to
> keep an O(n) operation O(n/2) or better, but it's not susceptible to
> this bug.
However, exist is not always neccessary (I formerly thought it is):
# perl -MData::Dumper -le 'my $hash = { u => x }; print "foo" if !
$hash->{a}; print Dumper($hash);'
foo
$VAR1 = {
'u' => 'x'
};
See, $hash->{a} hasnt been created :)
The code also has the problem that different subsystems might share the same
key, and thus advertise that somethin is there even though it isn't. Why
isnt sdl_config just a list (hash) of supported/unsupported things instead
a nested one?
E.g.
$sdl-config->{foo}->{barfel} = 1;
$sdl-config->{fub}->{barfel} = 0;
What if you now test for has('barfel'); Which one will come first!?
A flat structure would allow:
sub has
{
my ($class, $define) = @_;
return exists $sdl_config->{$define} ? $sdl_config->{$define} : undef;
}
which is much simpler.
> On the other hand, I suspect the new version performs better in list
> context.
In addition, there are like 10 different values, and it doesnt matter _at
all_ what you do with that hash in what order, since it is executed almost
always only once, and would in the worst case create a dozend hash keys (if
ever, see above).
This is not a place where you should optimize code and thus introduce bugs
in the code. :)
Cheers,
Tels
- --
Signed on Wed Feb 25 18:57:07 2004 with key 0x93B84C15.
Visit my photo gallery at http://bloodgate.com/photos/
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