I only used Guard for convenience. It can easily be replaced by

package My::Guard;
use strict;
sub new {
    bless $_[1] => $_[0];
};
sub DESTROY {
    $_[0]->()
};

[download]

The full (and really pure Perl) program then becomes:

#!perl -w
package My::Guard;
use strict;
sub new {
    bless $_[1] => $_[0];
};
sub DESTROY {
    $_[0]->()
};

package main;
use strict;

sub alias {\@_};
sub localize {
    my @values = @{ +pop }; # or any other convenient method
    my $aliases=alias(@_);
    my @saved= @_;

    #warn Dumper \@saved;
    $_[$_] = $values[$_] for 0..$#values;
    My::Guard->new(sub{
        $aliases->[$_]=$saved[$_] for 0..$#saved;
    })
};

my ($a,$b)=('a','b');

print "Start\n";
print qq($a $b),"\n";

my $restore=localize($a,$b,['foo','bar']);

print "Localized\n";
print qq($a $b),"\n";
undef $restore;
print "Restored\n";
print qq($a $b), "\n";

[download]

But still, you haven't convinced me that there are problems to which Scope::Upper is a good solution.

Update: As an afterthought, for somebody who thinks they need Scope::Upper, I think you should investigate the easier and potentially less powerful methods first, like having a destructor invoke a callback. I don't consider this a rare/outlandish technique, and there are many packages implementing this, like AtExit, Aspect::Guard, Scope::Guard and ReleaseAction.

Update2: Of course, this clever idea has a big drawback. It doesn't work for arrays and hashes.

In reply to Re^7: Scope::Upper localize? by Corion
in thread Scope::Upper localize? by Anonymous Monk

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