This is a follow up to Localizing hash keys in an AoH. tobyink's suggestion of guards has worked well, until I discovered I'd naively used the code in a case where I actually needed to delete the hash key/value pair when scope exited, instead of just restoring a value. I cobbled together the code 
sub localised_hashvalue {
    package localised::hashvalue;
    my ($ref, $key, $value) = @_;
    my $exist = exists $ref->{$key};
    my $old   = $ref->{$key};
    $ref->{$key} = $value;
    return bless [$ref, $key, $exist, $old];
    sub DESTROY {
        my ($ref, $key, $exist, $old) = @{+shift};
        $ref->{$key} = $old;
        delete $ref->{$key} if !$exist;
    }
}

[download]
which performs the necessary function, albeit in a clunkier-feeling way. The target hashrefs in the array are cross-referenced in a couple ways, so I really do need to localize the value in the hashref (as opposed to localizing an array slice and inserting duplicate hashrefs). Any ideas? Obviously this is more academic, since I have functioning code.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Localizing hash keys in an AoH, continued by kennethk

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