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[Robin Sheat]

Hey there,
I have a set of functions that send an XML element, wait for a response,
parse the response, and return it. However, there are often cases where
the resulting XML is never used, and so parsing it is pointless. Is
there a way that a sub can tell where the result is going to go, so that
it can not do the parsing if the result is going to be immediatly
discarded?

Something like this:
foo(a,b,c);
%result = foo(c,d,e);

sub foo {
...do stuff...
if (-result isn't discarded-) {
return parseResult($result);
}
}

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[Wolf Blaum]

> Hey there,
Hi

> I have a set of functions that send an XML element, wait for a response,
> parse the response, and return it. However, there are often cases where
> the resulting XML is never used, and so parsing it is pointless. Is
> there a way that a sub can tell where the result is going to go, so that
> it can not do the parsing if the result is going to be immediatly
> discarded?
>

If you are asking how to teel between:

$var=&sub;
and
&sub;

- not that I know.
However, there is a way to tell who asked for the result:
read perldoc -f caller

but why dont you pass a parameter to the sub that tells it?

Wolf

[Robin Sheat]

On Sat, Feb 14, 2004 at 08:19:20AM +0100, wolf blaum wrote:

> If you are asking how to teel between:
> $var=&sub;
> and
> &sub;

Pretty much, from the point of view of sub.

> However, there is a way to tell who asked for the result:
> read perldoc -f caller

Not really what I want.

> but why dont you pass a parameter to the sub that tells it?

Because there are about a dozen subs and I didn't want to change the API
on all of them, along with all the places they are being called from.
However, I resolved it, not quite so elegantly, but introducing a
'keepResults' method to the class that has the subs, which allows it to
be toggled. In my optimisation attempts I ended up stumbling into
another issue however, somewhat unrelated.

I set it up, so that if the results aren't needed, they aren't even read
from the network socket. This means that if the remote program is taking
its time to generate them, the Perl program doesn't have to wait for
data it'll be throwing away. I added a counter to see how much data we
are ignoring, so that when we finally do need something, we know how
much to discard. However, I found that if the the queue of data got
above one, one of two things happens: either the Java program at the
other end discards the extra XML elements sent to it while processing
ones that take a while, or replies get lost. Either way, the Perl end
sits there waiting for data that never arrives. If I can be bothered, I
might put debugging code into the Java to see whats happening, at that
end.

However, if anyone has a clue as to what's going please let me know (the
more data I can safely ignore, the faster my program can run :)

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[Jeff 'Japhy' Pinyan]

On Feb 14, Robin Sheat said:

>I have a set of functions that send an XML element, wait for a response,
>parse the response, and return it. However, there are often cases where
>the resulting XML is never used, and so parsing it is pointless. Is
>there a way that a sub can tell where the result is going to go, so that
>it can not do the parsing if the result is going to be immediatly
>discarded?

Yes, use wantarray().

sub foo {
if (not defined wantarray) { print "void context\n" }
elsif (wantarray) { print "list context\n" }
else { print "scalar context\n" }
}

foo();
$x = foo();
@y = foo();

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Jeff "japhy" Pinyan [email]japhy@pobox.com[/email] [url]http://www.pobox.com/~japhy/[/url]
RPI Acacia brother #734 [url]http://www.perlmonks.org/[/url] [url]http://www.cpan.org/[/url]
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]

[Robin Sheat]

On Sat, Feb 14, 2004 at 03:44:38AM -0500, Jeff 'japhy' Pinyan wrote:

> Yes, use wantarray().

Aha! Thanks :)

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