# Feature Proposal: Allow letter decrementing - Thread: https://externals.io/message/68160 - Original archive: https://news-web.php.net/php.internals/68160 - Started by Chris London on 2013-07-18T13:46:14+00:00 - Messages: 22 - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #68160 — Chris London — 2013-07-18T13:46:14+00:00 URL: https://externals.io/message/68160#68160 My friend shared some code with me today that wasn't working for him. He was incrementing letters like this: $letter = 'A'; echo ++$letter; // Output: B He was then trying to decrement letters like this: $letter = 'B'; echo --$letter; // Output: B He was really confused why his code wasn't working. Obviously the answer is, PHP doesn't support decrementing letters. My question is, why specifically doesn't it? It seems logical that if we support increment we should support decrement. My proposal: 1) Support decrementing letters - or - 2) Throw a notice explaining that decrementing is not supported so developers quickly know they can't do that One hiccup. I imagine maybe the reason we don't support decrementing is because what would happen if you tried to decrement 'A'. In that case I would suggest either returning `NULL` or throwing a notice. Thanks for the input Chris London --- ## #68161 — Mateusz Kocielski — 2013-07-18T14:20:58+00:00 URL: https://externals.io/message/68160#68161 · In reply to: #68160 > It seems logical that if we support increment we should support decrement. > > My proposal: > > 1) Support decrementing letters > - or - > 2) Throw a notice explaining that decrementing is not supported so > developers quickly know they can't do that > > One hiccup. I imagine maybe the reason we don't support decrementing is > because what would happen if you tried to decrement 'A'. In that case I > would suggest either returning `NULL` or throwing a notice. > > Thanks for the input > > Chris London Hello, Does anybody understand the rules behind the string incrementation? What's the explanation of following behaviour? '$x="ZZ";$x++;var_dump($x);' returns string(3) "AAA" '$x=" ZZ";$x++;var_dump($x);' returns string(3) " AA" Regards, Mateusz Kocielski --- ## #68162 — johannes@schlueters.de — 2013-07-18T14:33:40+00:00 URL: https://externals.io/message/68160#68162 · In reply to: #68160 > My friend shared some code with me today that wasn't working for him. He > was incrementing letters like this: > > $letter = 'A'; > echo ++$letter; // Output: B > > He was then trying to decrement letters like this: > > $letter = 'B'; > echo --$letter; // Output: B > > He was really confused why his code wasn't working. Obviously the answer > is, PHP doesn't support decrementing letters. Oviously this documented in http://de2.php.net/manual/en/language.operators.increment.php ;-) > My question is, why specifically doesn't it? > > It seems logical that if we support increment we should support decrement. ++$string; will always succeed. But what should $s = 'a'; --$s; result in? johannes --- ## #68163 — Xinchen Hui — 2013-07-18T14:37:49+00:00 URL: https://externals.io/message/68160#68163 · In reply to: #68161 在 2013-7-18，22:31，Mateusz Kocielski 写道： It seems logical that if we support increment we should support decrement. My proposal: 1) Support decrementing letters - or - 2) Throw a notice explaining that decrementing is not supported so developers quickly know they can't do that One hiccup. I imagine maybe the reason we don't support decrementing is because what would happen if you tried to decrement 'A'. In that case I would suggest either returning `NULL` or throwing a notice. Thanks for the input Chris London Hello, Does anybody understand the rules behind the string incrementation? What's the explanation of following behaviour? '$x="ZZ";$x++;var_dump($x);' returns string(3) "AAA" '$x=" ZZ";$x++;var_dump($x);' returns string(3) " AA" see http://www.php.net/manual/en/language.operators.increment.php thanks Regards, Mateusz Kocielski --- ## #68165 — Martin Amps — 2013-07-18T19:08:56+00:00 URL: https://externals.io/message/68160#68165 · In reply to: #68163 > One hiccup. I imagine maybe the reason we don't support decrementing is > because what would happen if you tried to decrement 'A'. In that case I > would suggest either returning `NULL` or throwing a notice. It would make sense to make it stay as ‘A’ like incrementing ‘Z' stays as ‘Z’. I do agree that string manipulation with arithmetic operators needs work/clarification. > 在 2013-7-18，22:31，Mateusz Kocielski 写道： > > It seems logical that if we support increment we should support decrement. > > > My proposal: > > > 1) Support decrementing letters > > - or - > > 2) Throw a notice explaining that decrementing is not supported so > > developers quickly know they can't do that > > > One hiccup. I imagine maybe the reason we don't support decrementing is > > because what would happen if you tried to decrement 'A'. In that case I > > would suggest either returning `NULL` or throwing a notice. > > > Thanks for the input > > > Chris London > > > Hello, > > Does anybody understand the rules behind the string incrementation? What's > the explanation of following behaviour? > > '$x="ZZ";$x++;var_dump($x);' returns string(3) "AAA" > '$x=" ZZ";$x++;var_dump($x);' returns string(3) " AA" > > see http://www.php.net/manual/en/language.operators.increment.php > > thanks > > Regards, > Mateusz Kocielski --- ## #68166 — Chris London — 2013-07-18T19:10:10+00:00 URL: https://externals.io/message/68160#68166 · In reply to: #68165 Something I learned today is incrementing 'Z' goes to 'AA' but that helps the point that it could use more work/clarification > One hiccup. I imagine maybe the reason we don't support decrementing is > because what would happen if you tried to decrement 'A'. In that case I > would suggest either returning `NULL` or throwing a notice. > > > It would make sense to make it stay as ‘A’ like incrementing ‘Z' stays as > ‘Z’. > > I do agree that string manipulation with arithmetic operators needs > work/clarification. > > > > 在 2013-7-18，22:31，Mateusz Kocielski 写道： > > It seems logical that if we support increment we should support decrement. > > > My proposal: > > > 1) Support decrementing letters > > - or - > > 2) Throw a notice explaining that decrementing is not supported so > > developers quickly know they can't do that > > > One hiccup. I imagine maybe the reason we don't support decrementing is > > because what would happen if you tried to decrement 'A'. In that case I > > would suggest either returning `NULL` or throwing a notice. > > > Thanks for the input > > > Chris London > > > Hello, > > Does anybody understand the rules behind the string incrementation? What's > the explanation of following behaviour? > > '$x="ZZ";$x++;var_dump($x);' returns string(3) "AAA" > '$x=" ZZ";$x++;var_dump($x);' returns string(3) " AA" > > see http://www.php.net/manual/en/language.operators.increment.php > > thanks > > Regards, > Mateusz Kocielski --- ## #68167 — Chris London — 2013-07-18T19:22:49+00:00 URL: https://externals.io/message/68160#68167 The one caveat about decrementing "A" and it goes to `NULL` is that if you increment `NULL` it goes to 1 so that may be confusing. We could also decrement "A" and it goes to `FALSE` and FALSE++ is still `FALSE` On Thu, Jul 18, 2013 at 1:10 PM, Phil Sturgeon wrote: > Incrementing "Z" results in "AA", because we're starting again. > Decrementing "A" should probably go to `NULL` as -A is no good. > > -- > Phil Sturgeon > > > > One hiccup. I imagine maybe the reason we don't support decrementing is > because what would happen if you tried to decrement 'A'. In that case I > would suggest either returning `NULL` or throwing a notice. > > > It would make sense to make it stay as ‘A’ like incrementing ‘Z' stays as > ‘Z’. > > I do agree that string manipulation with arithmetic operators needs > work/clarification. > > > > 在 2013-7-18，22:31，Mateusz Kocielski 写道： > > It seems logical that if we support increment we should support decrement. > > > My proposal: > > > 1) Support decrementing letters > > - or - > > 2) Throw a notice explaining that decrementing is not supported so > > developers quickly know they can't do that > > > One hiccup. I imagine maybe the reason we don't support decrementing is > > because what would happen if you tried to decrement 'A'. In that case I > > would suggest either returning `NULL` or throwing a notice. > > > Thanks for the input > > > Chris London > > > Hello, > > Does anybody understand the rules behind the string incrementation? What's > the explanation of following behaviour? > > '$x="ZZ";$x++;var_dump($x);' returns string(3) "AAA" > '$x=" ZZ";$x++;var_dump($x);' returns string(3) " AA" > > see http://www.php.net/manual/en/language.operators.increment.php > > thanks > > Regards, > Mateusz Kocielski --- ## #68176 — Sara Golemon — 2013-07-18T23:11:01+00:00 URL: https://externals.io/message/68160#68176 · In reply to: #68160 > My question is, why specifically doesn't it? > > Because Perl. --- ## #68177 — Chris London — 2013-07-18T23:18:09+00:00 URL: https://externals.io/message/68160#68177 · In reply to: #68176 I hear Perl 6 supports Str decrementing > > […] --- ## #68181 — Sherif Ramadan — 2013-07-19T05:37:25+00:00 URL: https://externals.io/message/68160#68181 · In reply to: #68177 > I hear Perl 6 supports Str decrementing > > I heard of Perl 6 once. --- ## #68182 — Mateusz Kocielski — 2013-07-19T06:39:45+00:00 URL: https://externals.io/message/68160#68182 · In reply to: #68163 > > […] > > see http://www.php.net/manual/en/language.operators.increment.php I don't see any explanation for the examples above. Documentation says: [...] For example, in PHP and Perl $a = 'Z'; $a++; turns $a into 'AA' [...] I'd expect " ZZ" to become " AAA" rather than " AA". I'm not sure if it's a bug in documentation, in code. Probably nobody can even distinguish if it's a bug or feature. Mateusz Kocielski --- ## #68183 — Yasuo Ohgaki — 2013-07-19T07:08:11+00:00 URL: https://externals.io/message/68160#68183 · In reply to: #68182 Hi, 2013/7/19 Mateusz Kocielski > > […] > > I don't see any explanation for the examples above. Documentation says: > > [...] For example, in PHP and Perl $a = 'Z'; $a++; turns $a into 'AA' [...] > > I'd expect " ZZ" to become " AAA" rather than " AA". I'm not sure if > it's a bug in documentation, in code. Probably nobody can even > distinguish if it's a bug or feature. > You may play with one liner. php -r "\$a = ' ZZ';for (\$i=0; \$i<100000000;\$i++) var_dump(++\$a);" This feature existed when I start using PHP3. Manual says > Note that character variables can be incremented but not decremented and > even so only plain ASCII characters (a-z and A-Z) are supported. Incrementing/decrementing > other character variables has no effect, the original string is unchanged. This behavior is due to the algorithm used for string ++/--. I think it looks at the end of char and tries to increment, but it finds non [a-zA-Z] char and stops operation. Therefore, it cycles over and over. It may seems strange, but I don't see reason to change. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net --- ## #68184 — Peter Lind — 2013-07-19T07:34:28+00:00 URL: https://externals.io/message/68160#68184 · In reply to: #68183 Interesting to note that although Perl 6 is apparently capable of decrementing strings, it doesn't fully mirror the incrementing: http://feather.perl6.nl/syn/S03.html#line_516 Specifically: decrementing 'AAA' would not turn into 'ZZ' but would error, according to that link -- WWW: plphp.dk / plind.dk CV: careers.stackoverflow.com/peterlind LinkedIn: plind Twitter: kafe15 > Interesting to note that although Perl 6 is apparently capable of > decrementing strings, it doesn't fully mirror the incrementing: > > http://feather.perl6.nl/syn/S03.html#line_516 > > Specifically: decrementing 'AAA' would not turn into 'ZZ' but would error, > according to that link > Carry handle of decrements is more complex than increments. It may be the reason. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net --- ## #68188 — Dan Cryer — 2013-07-19T09:18:39+00:00 URL: https://externals.io/message/68160#68188 · In reply to: #68187 What's the intended use case for string increment / decrement? It just seems like madness to me, using mathematical operators with strings, producing seemingly arbitrary results in some circumstances (C -> B -> A -> `NULL` / False ?). Also what happens in other languages? Take for example German, in which ß comes after S, Ü after U, and so on. > Hi, > > I take a look at the code. > It does support [0-9] also. > > [yohgaki@dev tests]$ php -r "\$a = ' a10';for (\$i=0; \$i<10;\$i++) > var_dump(++\$a);" > string(4) " a11" > string(4) " a12" > string(4) " a13" > string(4) " a14" > string(4) " a15" > string(4) " a16" > string(4) " a17" > string(4) " a18" > string(4) " a19" > string(4) " a20" > > It sounds good to have string decrements. > > > 2013/7/19 Peter Lind > > > […] > error, > > […] > > Carry handle of decrements is more complex than increments. > It may be the reason. > > Regards, > > -- > Yasuo Ohgaki > yohgaki@ohgaki.net > -- *Dan Cryer* 07590 698944 dan@dancryer.com +Dan @dancryer What's the intended use case for string increment / decrement? > + 1 could we please stop wasting time on such issues? many thanks > It just seems like madness to me, using mathematical operators with > strings, producing seemingly arbitrary results in some circumstances (C -> > B -> A -> `NULL` / False ?). > > Also what happens in other languages? Take for example German, in which ß > comes after S, Ü after U, and so on. > > > > > > […] > > > > -- > > *Dan Cryer* > > 07590 698944 > dan@dancryer.com > +Dan > @dancryer > -- 惠新宸 laruence Senior PHP Engineer http://www.laruence.com --- ## #68191 — Peter Lind — 2013-07-19T09:31:15+00:00 URL: https://externals.io/message/68160#68191 · In reply to: #68188 > What's the intended use case for string increment / decrement? > > Personally, I instantly think of mirroring spreadsheet columns - works quite well in that context. > It just seems like madness to me, using mathematical operators with > strings, producing seemingly arbitrary results in some circumstances (C -> > B -> A -> `NULL` / False ?). > > Throw a warning and don't decrement A/a any further - that's not arbitrary. > Also what happens in other languages? Take for example German, in which ß > comes after S, Ü after U, and so on. > > Nothing, works purely on ascii, as is currently the case. Perl handles other character sets though - see the link I posted for details on how. Regards Peter -- WWW: plphp.dk / plind.dk CV: careers.stackoverflow.com/peterlind LinkedIn: plind Twitter: kafe15 > > > > […] > Personally, I instantly think of mirroring spreadsheet columns - works > quite well in that context. > ++/-- 'XYZ00001234' would have use cases. > > > > […] > Throw a warning and don't decrement A/a any further - that's not arbitrary. > -- is more problematic. --'XYZ0000' would be 'XYZ0000' or 'XYY00000' or 'XYY'? It would be better not to change length of string, IMO. e.g. --'XYZ0000' became 'XYY0000' All chars would stop decrement at lowest chars of [0-9], [a-z], [A-Z]. e.g. Lowest value of 'XYZ0000' is 'AAA0000'. This is not a symmetric operation of ++, but it's impossible to achieve symmetric operation ++/-- on strings anyway. > > > […] > Nothing, works purely on ascii, as is currently the case. Perl handles > other character sets though - see the link I posted for details on how. > There may be need for this, but it will be very complex code than now. [0-9a-zA-Z] would be enough. PHP doesn't have default multibyte char module, too. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net --- ## #68193 — Nikita Popov — 2013-07-19T10:39:02+00:00 URL: https://externals.io/message/68160#68193 · In reply to: #68160 > My friend shared some code with me today that wasn't working for him. He > was incrementing letters like this: > > $letter = 'A'; > echo ++$letter; // Output: B > > He was then trying to decrement letters like this: > > $letter = 'B'; > echo --$letter; // Output: B > > He was really confused why his code wasn't working. Obviously the answer > is, PHP doesn't support decrementing letters. > > My question is, why specifically doesn't it? > > It seems logical that if we support increment we should support decrement. > > My proposal: > > 1) Support decrementing letters > - or - > 2) Throw a notice explaining that decrementing is not supported so > developers quickly know they can't do that > > One hiccup. I imagine maybe the reason we don't support decrementing is > because what would happen if you tried to decrement 'A'. In that case I > would suggest either returning `NULL` or throwing a notice. > > Thanks for the input > > Chris London > I don't think we should add string decrementing due to the rather complex logic behind it (imho the string incrementing that we have shouldn't be there either). What we *should* add though is a notice or warning in case an increment/decrement operation fails. incdec is one of the few places where we currently silently ignore FAILUREs, instead of throwing some helpful error message :) Nikita --- ## #68195 — Peter Lind — 2013-07-19T10:46:22+00:00 URL: https://externals.io/message/68160#68195 · In reply to: #68192 > Hi, > > 2013/7/19 Peter Lind > > > […] > > ++/-- 'XYZ00001234' would have use cases. > > > > […] > > -- is more problematic. > --'XYZ0000' would be 'XYZ0000' or 'XYY00000' or 'XYY'? > > php -r '$a = "YZ9"; var_dump(++$a);' gives me ZA0 If php -r '$a = "ZA0"; var_dump(--$a);' doesn't give YZ9 you'll just be left scratching your head. Granted, you might be left scratching your head as to why string incrementing works at all, but that can of worms was opened long ago. It would be better not to change length of string, IMO. > e.g. --'XYZ0000' became 'XYY0000' > > I'd go with --XYZ0000 -> XYY9999 Also, the string length shouldn't factor into it. > All chars would stop decrement at lowest chars of [0-9], [a-z], [A-Z]. > e.g. Lowest value of 'XYZ0000' is 'AAA0000'. > > This is not a symmetric operation of ++, but it's impossible to achieve > symmetric > operation ++/-- on strings anyway. > > Only at the edge case - and I personally can't see why that would mean asymmetric operation in the rest of the cases. -- WWW: plphp.dk / plind.dk CV: careers.stackoverflow.com/peterlind LinkedIn: plind Twitter: kafe15 > […] I once had an app which needed to generate long continuous ranges of alpha codes. But even then I did not implement -- in PHP userland. I think if there is a need for --, each application would need its own "correct" behaviour. AAA-- may be AA or ZZ or ZZZ or ZZ0 or ZZ9 or even 0ZZ depending on use case. If there is a reason to do this in C rather than PHP userland code, it's probably best fit in an extension. -- Ralf Lang Linux Consultant / Developer Tel.: +49-170-6381563 Mail: lang@b1-systems.de B1 Systems GmbH Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537 --- ## #68223 — Yasuo Ohgaki — 2013-07-19T20:45:23+00:00 URL: https://externals.io/message/68160#68223 · In reply to: #68193 Hi Nikita, 2013/7/19 Nikita Popov > I don't think we should add string decrementing due to the rather complex > logic behind it (imho the string incrementing that we have shouldn't be > there either). > Right. It is impossible to symmetric operation ++/-- for strings. Not implementing --'STRING' is a valid option. > What we *should* add though is a notice or warning in case > an increment/decrement operation fails. incdec is one of the few places > where we currently silently ignore FAILUREs, instead of throwing some > helpful error message :) > Making --'STRING' raises `E_NOTICE` is reasonable option. If PHP don't support, then it would better to notice users. It may be useful to spot bugs, too. Raising error might be more helpful for many users. I don't have concrete idea for --'STRING'. `E_NOTICE` might be the way to go. Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net