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Journal of IlyaM (2933)

Wednesday May 08, 2002
12:51 PM

Is it a number or a string?

[ #4768 ]
Coolest Perl trick I've learned recently:

sub is_numeric { ($_[0] & ~ $_[0]) eq "0"; }

I found this gem when I was reading this thread about DBI::PurePerl.

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  •   DB<8> p is_numeric(1.34)
    1
      DB<9> p is_numeric('1.34')

      DB<10>
    • It is based on the fact that operator '~' gives different result if it given string argument instead of numeric.

      DB<4> p ~ 100
      4294967195
      DB<5> p ~ '100'
      XXX

      where XXX some chars from second half of ASCII table.

      With numeric argument '~' acts as usual bitwise negation operator. With string argument it acts like

      join '', map chr((~ord) & 255), split //, $arg

      --

      Ilya Martynov (http://martynov.org/ [martynov.org])