in reply to Re^4: Incrementing a large number without Math::BigInt
in thread Incrementing a large number without Math::BigInt

Only auto-increment (++) is magical in that fashion and only when the variable is a "string". From perlop:

The auto-increment operator has a little extra builtin magic to it. If you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has been used in only string contexts since it was set, and has a value that is not the empty string and matches the pattern /^a-zA-Z*0-9*\z/, the increment is done as a string, preserving each character within its range, with carry: 
    print ++($foo = '99');      # prints '100'
    print ++($foo = 'a0');      # prints 'a1'
    print ++($foo = 'Az');      # prints 'Ba'
    print ++($foo = 'zz');      # prints 'aaa'

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The auto-decrement operator is not magical.
DWIM is Perl's answer to Gödel

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Re^6: Incrementing a large number without Math::BigInt
by ikegami (Patriarch) on Apr 26, 2006 at 05:17 UTC

    |, &, ^ and ~ also work on strings. 

    >perl -e "print 'A'|'B'
C
>perl -e "print 'C'&'E'
A
>perl -e "print 'A'^' '
a

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    I wish << and >> did as well.

    Documented in perlop

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      Yes, I actually noticed this node while searching for a solution to my problem. But isn't that more of an ASCII feature than a Perl one? I wonder why the deincrementing and bit shifting don't work.
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        ASCII has nothing to do with it. You can use those operators on any string of bytes, whether the data is ASCII, the result of inet_aton or a struct to pass to a system call. The operators work independantly of how the data is interpreted.

        Now, $letter ^ ' ' will not toggle the case of the letter in all encodings, but that's a (simple) algorithm that uses ^ and not ^ proper.

        Here's an example which demonstrates that ^ work no matter how the data was encoded: 

        use Socket qw( inet_aton inet_ntoa );

my $ip        = inet_aton('10.0.0.155');
my $mask      = inet_aton('255.255.255.240');
my $broadcast = $ip | ~$mask;

print(inet_ntoa($broadcast), "\n");  # 10.0.0.159

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        It's definitely a language feature, and I believe an uncommon one. You can't do that in C or Java, for example.

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