Re^8: Net::SSH2 test connection to remote host

In my opinion, DESTROY methods should not have side effects like changing $@ (or $? or $!), and if they do, it is a bug!

That's an opinion shared by others, but other people disagree. See for instance a thread about this on p5p this summer. Note that if DESTROY wouldn't propagate changes to $@, $! or $? DESTROY would be different from other functions, because $@, $! and $? behave differently. It also means you can have code that throws an exception, but afterwards $@ isn't set (your local $@ suffers from the same problem):

    sub one::DESTROY {
        die "foo\n";
    }
    eval {my $x = bless [], 'one'};
    say "\$\@ = $@";
    __END__
    $@ =     (in cleanup) foo
[download]

but

    sub one::DESTROY {
        local $@;
        die "foo\n";
    }
    eval {my $x = bless [], 'one'};
    say "\$\@ = $@";
    __END__
    $@ =
[download]

This is far from ideal as well, and I doubt it's much better than the current situation.

People have suggested a new variable, @@, where new errors get pushed onto, instead of having them override $@. But noone has written a patch to actually do this.

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Re^9: Net::SSH2 test connection to remote host by salva (Canon) on Oct 01, 2008 at 10:30 UTC
ok, let me refine my comment: DESTROY methods should not have side effects like changing $@ unless they do it while `die`ing In other words, I have no problem if some DESTROY method `die`s and changes $@ while doing it. In practice, what I mean is that inside a DESTROY sub, if `eval` is used, `$@` should be localized for its scope (and the same applies for `$!` and IO operations and `$?` and `system, fork`, etc.) For instance, I see no problem with this DESTROY method: `sub DESTROY { my $self = shift; { local $@; eval { $self->whatever() }; } die "cleanup failed" unless $self->cleanup; }` [download] Regarding the p5p discussion, it was about whether this no-side-effects-from-DESTROY thing should be implemented at the interpreter level.	[reply] [d/l] [select]

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Re^9: Net::SSH2 test connection to remote host
by salva (Canon) on Oct 01, 2008 at 10:30 UTC

DESTROY methods should not have side effects like changing $@ unless they do it while dieing

In other words, I have no problem if some DESTROY method dies and changes $@ while doing it.

In practice, what I mean is that inside a DESTROY sub, if eval is used, $@ should be localized for its scope (and the same applies for $! and IO operations and $? and system, fork, etc.)

For instance, I see no problem with this DESTROY method:

sub DESTROY {
  my $self = shift;
  { local $@; eval { $self->whatever() }; }
  die "cleanup failed" unless $self->cleanup;
}
[download]

Regarding the p5p discussion, it was about whether this no-side-effects-from-DESTROY thing should be implemented at the interpreter level.

[reply]
[d/l]
[select]