string operations of arithmetic

xiaoyafeng has asked for the wisdom of the Perl Monks concerning the following question:

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
[download]

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?

I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction

Comment on string operations of arithmetic Download Code

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Re: string operations of arithmetic by choroba (Cardinal) on Jun 24, 2011 at 12:37 UTC
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'` [download]	[reply] [d/l] [select]
Re: string operations of arithmetic by MidLifeXis (Monsignor) on Jun 24, 2011 at 12:48 UTC
`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. --MidLifeXis	[reply] [d/l] [select]
Re: string operations of arithmetic by Anonymous Monk on Jun 24, 2011 at 12:26 UTC
read perlnumber, cause strings are strings until you put them in numeric context	[reply]
Re: string operations of arithmetic by wind (Priest) on Jun 24, 2011 at 16:24 UTC
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.	[reply]