Error.pm vs closure issue fixed in Perl

npf has asked for the wisdom of the Perl Monks concerning the following question:

Hello !

I recently began to play with Perl exception mechanisms, and gave a try to the Error module with the "try/catch" syntax.
However, reading docs ( Matt Sergeant presentation), I discovered that it presents a serious issue with regard to closures, and creates memory leaks.
But I also read in the DDJ article from Dave Rolsky that Perl >= 5.8.4 might fix the closure issue ?
Trying the test sample provided in the presentation:

#!/usr/bin/perl -w
use strict;
use warnings;

use Error qw(:try);
for (1..3) {
    my $x = Foo->new();
    try {
        try { print "$_: $x\n" };
    };
}
END { warn("interpreter exit\n") }
package Foo;
sub new { return bless {}, shift }
sub DESTROY { warn("Foo::DESTROY\n") }
[download]

I indeed notice that the output result changes between perl 5.6.1:

1: Foo=HASH(0x80f6084)
2: Foo=HASH(0x813b750)
3: Foo=HASH(0x815a0f0)
interpreter exit
Foo::DESTROY
Foo::DESTROY
Foo::DESTROY
[download]

and Perl 5.10.0:

1: Foo=HASH(0x81981f8)
Foo::DESTROY
2: Foo=HASH(0x81981f8)
Foo::DESTROY
3: Foo=HASH(0x81981f8)
Foo::DESTROY
interpreter exit
[download]

The object seems indeed destroyed when leaving the loop's scope.

Can we then consider that this closure issue when using the "try/catch" syntax of the Error package is over ? Is it now advisable to use the Error module with the "try/catch" syntax ?

Nothing appears indeed in the perl584delta.pod about closures.

Regards,
Pierre

Comment on Error.pm vs closure issue fixed in Perl > 5.8.4 ? Select or Download Code

Replies are listed 'Best First'.
Re: Error.pm vs closure issue fixed in Perl > 5.8.4 ? by perrin (Chancellor) on Sep 02, 2008 at 01:37 UTC
That problem does seem to be fixed, but returning from inside a try block is still a problem (and not fixable as long as try blocks are implemented as sub refs), so I would still avoid this module. See Re: Re2: Learning how to use the Error module by example for a full example and look at Exception-Class-TryCatch for an alternative.	[reply]
Re^2: Error.pm vs closure issue fixed in Perl > 5.8.4 ? (return) by tye (Sage) on Sep 02, 2008 at 20:42 UTC
but returning from inside a try block is still a problem (and not fixable as long as try blocks are implemented as sub refs), returning from a 'try' block is not fixable at all. Because 'try' has to be implemented via eval and return in an eval just leaves the eval, it doesn't return from the enclosing subroutine. So this particular problem is a problem with Perl(5)'s implementation of exceptions and not at all a problem specific to Error.pm. For the problem with Error.pm, `s/try/catch/g` on your statement: but returning from inside a catch block is still a problem (and not fixable as long as catch blocks are implemented as sub refs), - tye	[reply]
Re^3: Error.pm vs closure issue fixed in Perl > 5.8.4 ? (return) by perrin (Chancellor) on Sep 02, 2008 at 21:37 UTC
Interesting, I thought that eval would allow a return, but you're right, it doesn't. So there are two problems that prevent this from working intuitively with return statements and neither of them have any known fix in Perl 5.	[reply]