string operations of arithmetic

[xiaoyafeng]

here is code:

perl -e "$a = qq(ab); $a + 3; print $a;"  # ab

perl -e "$a = qq(ab1); $a ++; print $a;"   # ab2

perl -e "$a = qq(ab1); for(1..10) {$a ++;} print $a;" #ac1

looks like perl5 string doesn't support operations of arithmetic but self-increment/decrement. My question is how override operator so as to fit on string? and take a look third statement, IMHO, ab11 is more reasonable. Any help?

[choroba]

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'

[MidLifeXis]

perl -e "$a = qq(ab); $a + 3; print $a;"  # ab

No. You didn't assign the results of $a + 3 back to $a, so I don't know what you would have expected it to do. The results I would expect would be 3

IMHO, ab11 is more reasonable.

This is documented in perlop (search for "Auto-increment"). The critical portion is:

the increment is done as a string, preserving each character within its range, with carry [emphasis added]

If it were implemented the way you propose, then the with carry part would no longer be valid. Since you are able to just do a string append of a numeric value to implement your use case ($base . $counter++), and it becomes much more difficult to do the string carry use case, IMHO it makes much more since to implement the string increment magic^* as it currently stands.

^* I am not arguing for, or against, the string magic increment here, as I have not given enough thought to make an argument considering both sides. However, I can point to cases where I have used it in the past.

[Anonymous Monk]

read perlnumber, cause strings are strings until you put them in numeric context

[wind]

As others have already said, your statements work as spec'd in perlop - Auto increment/decrement.

If you'd like them to work in a different way, you must simply overload those operations in a class.