use Devel::LexAlias

[tobyink]

This is a second attempt at a fix for #2 using Devel::LexAlias.

It has a fallback to using package variables when Devel::LexAlias is not available, because I think it's nice to have a pure Perl implementation. The two code paths only diverge in a couple of very small places, so I don't think it should have much impact on Eval::Closure's maintainability.

[doy]

I still don't like the global variable idea. For instance:

#!/usr/bin/env perl
use strict;
use warnings;
use Test::More;

use Eval::Closure;

my $destroyed = 0;

package Foo {
    sub DESTROY { $destroyed++ }
}

{
    my $number  = bless \(my $foo), "Foo";
    $$number = 40;
    my $closure = eval_closure(
            source       => 'sub { $$xxx += 2 }',
            environment  => { '$xxx' => \$number },
    );

    $closure->();

    is($$number, 42);
    is($destroyed, 0);
}
is($destroyed, 1);

done_testing;

There are a lot of ways that global variables don't behave the same way as lexical variables do, and I don't want to have to deal with all of that and end up breaking in a bunch of different edge cases.

[tobyink]

Hmmm... good point.

[tobyink]

I do actually have another a pure Perl fallback solution (using tied lexicals) if you're interested.

[doy]

Not particularly, that would be even more broken (you wouldn't be able to close over existing tied variables anymore, for instance). Maybe aliasing should just be an option, that dies if Devel::LexAlias isn't installed?

[tobyink]

I have a test case with a tied scalar that works. I'm not doing anything especially interesting in the tied object; just:

my @store;

{
    package MyTie;
    use Tie::Scalar ();
    our @ISA = 'Tie::StdScalar';
    sub STORE {
        my $self = shift;
        push @store, $_[0];
        $self->SUPER::STORE(@_);
    }
}

[tobyink]

The only place it fails is if you call tied($closed_over), you get back the hacky-hack tied object rather than getting back what you should get back.

[doy]

On Thu, Jul 25, 2013 at 12:20:47PM -0700, Toby Inkster wrote:

The only place it fails is if you call tied($closed_over), you get
back the hacky-hack tied object rather than getting back what you
should get back.

I imagine it'll also fail if you untie the original variable outside of
the closure, or tie it to something else.

Basically, if this is going to be an implicit decision based only on
whether or not Devel::LexAlias is installed, it has to either produce
identical results in all cases, or die. I really don't want "almost the
same, except breaks in edge cases" when running identical code in
different environments.

[tobyink]

I imagine it'll also fail if you untie the original variable outside of the closure, or tie it to something else.

No, that all works fine.

[doy]

My second point still stands.

[tobyink]

This is all quite academic anyway - the pull request as it stands doesn't include the fallback to tie.

[doy]

Thinking about this some more, I think this should probably be an alias => 1 option rather than default behavior, at least for now. This preserves backwards compatibility, and allows the module to remain pure-perl by default (the alias option should start by doing something like die unless eval { require Devel::LexAlias }).

[tobyink]

OK; I'll sort that out tomorrow.

[tobyink]

Done.

[doy]

Thanks, that looks good.