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Re^2: The Null Mull (or, when OO needs more O)

by diotalevi (Canon)
on Nov 29, 2004 at 21:49 UTC ( #411053=note: print w/ replies, xml ) Need Help??


in reply to Re: The Null Mull (or, when OO needs more O)
in thread The Null Mull (or, when OO needs more O)

undef isn't normally an lvalue. How about trying that as ${ \ undef } = ... instead?


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Re^3: The Null Mull (or, when OO needs more O)
by hardburn (Abbot) on Nov 29, 2004 at 21:52 UTC

    Still no:

    BEGIN { &Internals::SvREADONLY(\undef, 0); ${ \undef } = 42; &Internals::SvREADONLY(\undef, 1); } my $x = undef; print( ((undef) ? 'True' : 'False'), $/); print( ((defined undef) ? 'True' : 'False'), $/); print( (($x) ? 'True' : 'False'), $/); print( ((defined $x) ? 'True' : 'False'), $/); print $x; __OUTPUT__ True True False False

    "There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.

      Aha. my $x = undef wasn't as simple as we thought. $x was being cleared without PL_undef actually being assigned. Swap the right side for something more complicated like $hash{'non-existant'} and you'll find that $x is now 42.
        That's a pity ... I thought the undef function was supposed to return PL_undef if you passed it no parameters. At least, that's what the Perl cookbook implies on p369, as well as the Camel in its discussion of the undef function in the Appendices. Why wouldn't it work? (And, yes, I'm scared of spelunking the Perl codebase.)

        Being right, does not endow the right to be rude; politeness costs nothing.
        Being unknowing, is not the same as being stupid.
        Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
        Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

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