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Re: The best "true zero" is...

by mce (Curate)
on Jun 08, 2005 at 08:41 UTC ( #464589=note: print w/replies, xml ) Need Help??

in reply to The best "true zero" is...

Isn't 0E0 and "Larry's 0 but true" the same? :-)

Dr. Mark Ceulemans
Senior Consultant
BMC, Belgium

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Re^2: The best "true zero" is...
by tbone1 (Monsignor) on Jun 09, 2005 at 13:04 UTC
    Isn't 0E0 and "Larry's 0 but true" the same? :-)

    Not at all. "0 but true" describes a state of data in Perl. "0E0" is part of the lyrics for the background singers in "Jungle Love" by Morris Day and the Time. Quite different.

    tbone1, YAPS (Yet Another Perl Schlub)
    And remember, if he succeeds, so what.
    - Chick McGee

Re^2: The best "true zero" is...
by ambrus (Abbot) on Jun 08, 2005 at 11:28 UTC

    No, it's really the string "0 but true". Try this for example:

    use File::Temp; $th = File::Temp::tempfile(undef, "UNLINK", 1); $zbt = + sysseek $th, 0, 0; print $zbt, "\n";

    The "E0" suffix appears with the flip-flop operators, but "0E0" can never appear, only "1E0", "2E0" etc.

      true, but also not true :-)

      Many functions -like the execute function in DBI- return 0E0 when they want to return a result that is ment to be zero but is 'boolean' true in tests

      So, indeed it is not general perl, but it is common to use 0E0 as "zero but true".


      Dr. Mark Ceulemans
      Senior Consultant
      BMC, Belgium

        That's right, but the core perl uses only "0 but true", so "0E0" is not Larry's.

Re^2: The best "true zero" is...
by ikegami (Pope) on Jul 28, 2010 at 16:35 UTC


    $ perl -wle'print "0 but true" eq "0E0" ?1:0' 0

    They are both silently equal to zero yet true, but so are the other poll options (except "0x0").

    $ perl -wle'print 0+"0 but true"' 0 $ perl -wle'print 0+"0E0"' 0 $ perl -wle'print "0 but true" ?"true":"false"' true $ perl -wle'print "0E0" ?"true":"false"' true

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[Corion]: hippo: If you have a Unicode-wise Perl then likely some zero-width characters in $x would work. Maybe $x = "\x{200b}" works.
[Corion]: Hmm - no, that outputs 1 for me on 5.14 - perl -wle "my $x = qq(\x{200b}); warn $x; warn length $x"
[hippo]: Smart - I'll give that a go. Thanks.
[hippo]: Ah
[Corion]: But maybe there is some other Unicode string that will be true but have a zero width
[hippo]: For explanation, I've seen this construct in someone else's code (no names, no pack drill) and couldn't think of a situation to trigger it.
[Corion]: You'll have to look somewhere esoteric for that. Maybe some tied variable or special dualvar can also trigger that. But it's certainly not a common occurrence
[Corion]: And on 5.20, the following also outputs no find:perl -wle 'for my $x ("\x{2000}".."\ x{1fffff}") { if( $x && ! length $x ) { warn qq(<$x>); warn length $x; die } }'
[Corion]: (this time on Unix)
[hippo]: Understood. I'll have to go through the code and see if it's doing anything fancy with ties, dual-vars or non-scalars. In the end, it's probably a bug though.

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