# Allowing variable strings to be defined for a string offset - Thread: https://externals.io/message/107915 - Original archive: https://news-web.php.net/php.internals/107915 - Started by George Peter Banyard on 2019-12-16T09:58:34+00:00 - Messages: 4 - 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 --- ## #107915 — George Peter Banyard — 2019-12-16T09:58:34+00:00 URL: https://externals.io/message/107915#107915 Greetings internals, I'm here to get internals's opinion about allowing a string offset to be replaced with arbitrary strings. Since forever strings with more then one byte have been truncated silently to one byte. The case with empty string *kinda* was existent but had a buggy behaviour (see bug 71572 [1]) and as such has been turned into a warning in PHP 7.1.0, and is meant to be promoted to an Error Exception per the Reclassifying engine warnings RFC. [2] An illustration of both these cases is available on 3v4l.org [3] I've got an implementation ready as a pull request on GitHub [4] (which still needs some polishing for it to make CI happy and fix the various leaks). However, the question is if this behaviour is desirable. Moreover, the silent truncation of strings with more than one byte should be changed to the same severity as the empty string case; i.e. an Error Exception. This seems reasonable due to the possible loss of data. What ever the decision is, a BC break is to be expected. As code which inadvertently tries to assign multiple bytes to an offset will know have all those bytes in the string whereas before only the first one was used to replace the byte at the designated offset. On the other hand the introduction of an Error Exception is obviously a BC break but as it points out to some kind of logic error. I would assume the impact to be minimal for both of these case. Any opinions? Best regards George Peter Banyard [1] https://bugs.php.net/bug.php?id=71572 [2] https://wiki.php.net/rfc/engine_warnings [3] https://3v4l.org/O0nEM [4] https://github.com/php/php-src/pull/5013 --- ## #107917 — Claude Pache — 2019-12-16T11:20:42+00:00 URL: https://externals.io/message/107915#107917 · In reply to: #107915 > Le 16 déc. 2019 à 10:58, George Peter Banyard a écrit : > > Greetings internals, > > I'm here to get internals's opinion about allowing a string offset to be > replaced with arbitrary strings. > > Since forever strings with more then one byte have been truncated silently > to one byte. The case with empty string *kinda* was existent but had a > buggy behaviour (see bug 71572 [1]) and as such has been turned into a > warning in PHP 7.1.0, and is meant to be promoted to an Error Exception per > the Reclassifying engine warnings RFC. [2] > An illustration of both these cases is available on 3v4l.org [3] > > > I've got an implementation ready as a pull request on GitHub [4] (which > still needs some polishing for it to make CI happy and fix the various > leaks). > > However, the question is if this behaviour is desirable. Moreover, the > silent truncation of strings with more than one byte should be changed to > the same severity as the empty string case; i.e. an Error Exception. This > seems reasonable due to the possible loss of data. > > What ever the decision is, a BC break is to be expected. As code which > inadvertently tries to assign multiple bytes to an offset will know have > all those bytes in the string whereas before only the first one was used to > replace the byte at the designated offset. On the other hand the > introduction of an Error Exception is obviously a BC break but as it points > out to some kind of logic error. > I would assume the impact to be minimal for both of these case. > > Any opinions? > > Best regards > > George Peter Banyard > > [1] https://bugs.php.net/bug.php?id=71572 > [2] https://wiki.php.net/rfc/engine_warnings > [3] https://3v4l.org/O0nEM > [4] https://github.com/php/php-src/pull/5013 Being able to replace one byte with an arbitrary string does not seem very useful to me, unless you add the functionality of replacing an arbitrary substring with an arbitrary string (an equivalent of `array_splice()` for strings). Your implementation gives the following potentially surprising result: IMO, the only reasonable thing to do at this point is just emitting a Warning (or an Error). —Claude --- ## #107918 — michal.brzuchalski@gmail.com — 2019-12-17T07:06:32+00:00 URL: https://externals.io/message/107915#107918 · In reply to: #107915 pon., 16 gru 2019 o 10:58 George Peter Banyard napisał(a): > Greetings internals, > > I'm here to get internals's opinion about allowing a string offset to be > replaced with arbitrary strings. > > Since forever strings with more then one byte have been truncated silently > to one byte. The case with empty string *kinda* was existent but had a > buggy behaviour (see bug 71572 [1]) and as such has been turned into a > warning in PHP 7.1.0, and is meant to be promoted to an Error Exception per > the Reclassifying engine warnings RFC. [2] > An illustration of both these cases is available on 3v4l.org [3] > > > I've got an implementation ready as a pull request on GitHub [4] (which > still needs some polishing for it to make CI happy and fix the various > leaks). > > However, the question is if this behaviour is desirable. Moreover, the > silent truncation of strings with more than one byte should be changed to > the same severity as the empty string case; i.e. an Error Exception. This > seems reasonable due to the possible loss of data. > > What ever the decision is, a BC break is to be expected. As code which > inadvertently tries to assign multiple bytes to an offset will know have > all those bytes in the string whereas before only the first one was used to > replace the byte at the designated offset. On the other hand the > introduction of an Error Exception is obviously a BC break but as it points > out to some kind of logic error. > I would assume the impact to be minimal for both of these case. > > Any opinions? > > Best regards > > George Peter Banyard > > [1] https://bugs.php.net/bug.php?id=71572 > [2] https://wiki.php.net/rfc/engine_warnings > [3] https://3v4l.org/O0nEM > [4] https://github.com/php/php-src/pull/5013 Allowing to unset string offset with empty string assignment in your patch will not trigger a Warning anymore, but using unset with string offset currently emits "Fatal error: Uncaught Error: Cannot unset string offset". An expected result is to be the same but an effect radically different as you can see [1]. IMHO allowing string offset to be unset using unset construct could be allowed to ensure consistency then. Any thoughts on this? BR, -- Michał Brzuchalski [1] https://3v4l.org/0Ol3N --- ## #107929 — Nikita Popov — 2019-12-19T13:18:00+00:00 URL: https://externals.io/message/107915#107929 · In reply to: #107917 On Mon, Dec 16, 2019 at 12:21 PM Claude Pache wrote: > > > > […] > : > > […] > silently > > […] > per > > […] > to > > […] > points > > […] > > > Being able to replace one byte with an arbitrary string does not seem very > useful to me, unless you add the functionality of replacing an arbitrary > substring with an arbitrary string (an equivalent of `array_splice()` for > strings). Your implementation gives the following potentially surprising > result: > > $str = "Hello world"; > var_dump(strlen($str)); // 11 > $str[0] = "あ"; // replace the first byte with three bytes (assuming source > code is UTF-8-encoded) > $str[0] = "H"; // replace the first byte with one byte > var_dump(strlen($str)); // 13 > ?> > > IMO, the only reasonable thing to do at this point is just emitting a > Warning (or an Error). > I agree. As it's currently silently accepted, I'd recommend starting with a warning. Nikita