in reply to Dangerous Names

"Nan McEntire" get numified to NaN on some systems, and the NaN check apparently causes <=> to return undef. 

$ perl -MDevel::Peek -e'Dump(0 <=> "Nan McEntire")'
SV = NULL(0x0) at 0x503848
  REFCNT = 2147483621
  FLAGS = (PADBUSY,PADTMP,READONLY)

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Re^2: Dangerous Names
by samtregar (Abbot) on Dec 17, 2008 at 22:07 UTC
    Right, that's half the battle. Furthermore, sort barfs on undefs, which I find very odd. Pretty much everything else in Perl is happy to treat undef as 0, why not sort?

    -sam

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      Pretty much everything else in Perl is happy to treat undef as 0, why not sort?
      I think you're confused 
      D:\>perl -wle"print undef"
Use of uninitialized value in print at -e line 1.

D:\>perl -wle"warn undef"
Use of uninitialized value in warn at -e line 1.

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      Nothing in perl treats undef as 0 without barfing 
      D:\>perl -we"print 1 <=> undef
Use of uninitialized value in numeric comparison (<=>) at -e line 1.
1
D:\>perl -we"print 1 + undef
Use of uninitialized value in addition (+) at -e line 1.
1
D:\>perl -we"print 1 - undef
Use of uninitialized value in subtraction (-) at -e line 1.
1
D:\>

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        >> Pretty much everything else in Perl is happy to treat undef as 0, why not sort?
        > I think you're confused
        [...]
        These are just warnings. sort dies, that's the difference. So if you don't have warnings on, you can do string comparisons with <=> as long as you want, and suddenly with a special input your script will die instead of only warn.
        I see it as another encouragement to always use warnings =)
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