(This is with 5.8.8 on OSX.)

I'm working on getting DBM::Deep to properly handle a edgecase and I ran into an edgecase with overload and re-blessing objects. The code below demonstrates the problem. 

{
    package Null;
    use overload
        bool => sub { undef },
        '""' => sub { undef },
        '0+' => sub { undef },
        fallback => 1,
        nomethod => 'AUTOLOAD';

    sub AUTOLOAD { return; }
}

{
    package Foo;
    sub new { return bless { a => 'b' }, shift; }
    sub apple { 'pear' }
}

my %x = (
    foo => Foo->new,
);
my $y = $x{foo};
print "Y1: $y\n";

bless $x{foo}, 'Null';
%{$x{foo}} = ();

print "Y2: $y\n";
my $z = $x{foo};
print "Z: $z\n";

[download]
What I'm seeing: 
Y1: Foo=HASH(0x1801234)
Y2: Null=HASH(0x1801234)
Z:

[download]
I would expect Y2 and Z to be the same. It's as if the overloading doesn't happen unless the SV is created after the blessing. Reblessing doesn't seem to trigger the overloading. Am I missing something?

For the record, what I'm trying to do is fix the following edgecase: 

$db->{foo} = { a => 'b' };
my $x = $db->{foo};
my $y = $db->{foo};
ok( $x == $y ); # This is broken in 1.0004 and before, but fixed in SV
+N.

delete $db->{foo};
is( $x, undef ); # This works
is( $x + 0, 0 ); # This does not

[download]
If someone has an idea of how to fix the underlying issue, I'm all ears.
My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Overload + reblessing oddity by dragonchild

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.