How can I serialize a closure in Perl? - perl

Question

I think this might be best asked using an example:
use strict;
use warnings;
use 5.010;
use Storable qw(nstore retrieve);
local $Storable::Deparse = 1;
local $Storable::Eval = 1;
sub sub_generator {
my ($x) = #_;
return sub {
my ($y) = #_;
return $x + $y;
};
}
my $sub = sub_generator(1000);
say $sub->(1); # gives 1001
nstore( $sub, "/tmp/sub.store" );
$sub = retrieve("/tmp/sub.store");
say $sub->(1); # gives 1
When I dump /tmp/sub.store I see:
$VAR1 = sub {
package Storable;
use warnings;
use strict 'refs';
my($y) = #_;
return $x + $y;
}
But $x is never defined in this sub. I would expect that the sub generated by sub_generator will have $x replaced with its actual value upon generation. How should I solve this?
Note this question relates to this one.

Answer 1

Unfortunately I don't think Storable works with closures. However there are other CPAN modules that will serialise a closure. For eg. Data::Dump::Streamer
use 5.012;
use warnings;
use Data::Dump::Streamer;
sub sub_generator {
my ($x) = #_;
return sub {
my ($y) = #_;
return $x + $y;
};
}
my $sub = sub_generator(1000);
say $sub->(1); # gives 1001
my $serialised = Dump( $sub )->Out;
my $copy = do {
my $CODE1 = undef;
eval $serialised;
$CODE1;
};
say $copy->(2); # gives 1002
say $sub->(1); # still gives 1001
This is what the serialised code looks like when printed here, say Dump $sub;:
my ($x);
$x = 1000;
$CODE1 = sub {
use warnings;
use strict 'refs';
BEGIN {
$^H{'feature_unicode'} = q(1);
$^H{'feature_say'} = q(1);
$^H{'feature_state'} = q(1);
$^H{'feature_switch'} = q(1);
}
my($y) = #_;
return $x + $y;
};
Update
See this thread Storable and Closures on the Perl5 porters mailing list. It confirms what I thought about Storable and closures.
/I3az/