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Postings from January 2011
Abigail <abigail <at> abigail.be> writes: >>| 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: > Note that the documentation the quote contains a couple of white lies. > > $a = "foo123"; > 0 + $a; # Use the variable $a in numeric context > $b = $a; > $a = "bar456"; > $a ++; > $b ++; > say $a; # Prints 'bar457'; > say $b; # Prints '1'; The documentation is a little inconsistent; $a 'has ever been used in a numeric context', but also 'has been used only in string contexts since it was set'. So either case could apply. Rather than these mealy-mouthed ways of hinting at the internal state of a scalar, it might be better to come out and expose the dual-valued nature of scalars to the programmer, so you can say 'when done on strings, ++ has some magic, and when done on numbers, it adds one'. But that would require quite a change to the way we think about Perl programming. The casual Perl coder is not really aware of when a scalar is represented as a string or number, and usual tutorial material does not encourage thinking about it. -- Ed Avis <eda@waniasset.com>Thread Previous | Thread Next