Re: [PHP-DEV] SPL development interest

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  110166
May 15, 2020 11:53 Danack@basereality.com (Dan Ackroyd)
On Thu, 14 May 2020 at 19:14, Jakob Givoni <jakob@givoni.dk> wrote:
> > Hi Internals, >
Hi Jakob, Obviously, all of the following is my own personal opinion, and other people may have different opinions. There are two main lessons learnt from the SPL experience. i) Some APIs need to evolve separately from the PHP release schedule*. As otherwise any mistake in the design of the API is locked in until the next minor release. ii) PHP needs a better way of installing extensions. There was a lot of work done on this in https://github.com/FriendsOfPHP/pickle but that effort seems to have been abandoned after a huge amount of work was done for it. If anyone has any info on what the problems were with the approach taken in that project, sharing that knowledge with the rest of the PHP community would be helpful in a new attempt to solve that problem. To answer your questions:
> - What is the status of this extension currently? Is it being actively developed or just supported?
It's pretty dead and the code is quite scary to even touch.
> - Is there any interest in adding stuff here - f.ex. new classes, interfaces or traits?
Absolutely no interest for me. As I said, new attempts to provide common libraries should be done separately from PHP core. Preferably in userland code where possible.
> And technically, how is something like ArrayObject class implemented? And should you implement it again, would it be done the
same way? The code is in: https://github.com/php/php-src/blob/d7f7080bb5b42a4dd2d08c91c02645b9d9a74a50/ext/spl/spl_array.c And a different approach should be taken. I've posted some notes of my thoughts on the individual parts of the SPL below. cheers Dan Ack ## Iterators These are quite useful, though possibly could do with a better developer experience around using them. The file related ones are best avoided though - see File Handling below. ## Datastructures People tend not to use them, but it is hard to express exactly why. It is partly due to some issues in their implementations. For example that the function [splpriorityqueue.recoverfromcorruption](https://www.php.net/manual/en/splpriorityqueue.recoverfromcorruption.php) exists is a pretty bad sign. There are a better set of datastructures available in the [Ds extension](https://github.com/php-ds/ext-ds). I think possibly it is related about the difficulty in converting from arrays to custom data structures and back again, being a not good experience. ## Exceptions The attempt has two fundamental mistakes in my opinion. First, I think all exceptions should extend a base exception that is specific to the library that the code is in. e.g. try { $image = new Imagick("foo.png"); $image->someMethodThatMightThrow(); } catch (ImagickException $e) { // This catch should be guaranteed to catch all exceptions // that could possibly be thrown by 'someMethodThatMightThrow' } Any exceptions to that rule, like a TypeError that is not caught internally and rethrown with an Imagick specific version, should be considered as a bug. Second, having a hierarchy of exceptions that builds up more specific meaning is something that has a strong aesthetic appeal to developers, but has no actual benefit. Other than extending a base exception for that library. ## File Handling There are multiple issues for them. They are not well designed classes, are kind of difficult to work with, and also some of the assumptions in them are unsafe. For example cloning a FileSystemIterator assumes that the directory has not changed: https://bugs.php.net/bug.php?id=69291 More fundamentally I think these classes are also a mistake. Here is a quote from a paper by Edsger W. Dijkstra*:
> the purpose of abstracting is not to be vague, but to create > a new semantic level in which one can be absolutely precise.
I think this can be turned round the other way. If an abstraction does not provide a new, more precise semantic level, then it does not provide any value. Those classes are not simpler to use than the low level unix file handling routines. And so they do not provide any value over just using the low level functions. In fact they are harmful as they hide some details that you probably want to know about. That is an opinion that I think also applies to the idea of providing an OO api to the functions for handling http requests, e.g. get_headers(). Although they could do with improvement through having less magic, and being more complete (e.g. why isn't there a get_body() function?) putting them all in an OO api seems the wrong thing to do to me. cheers Dan Ack * Edsger W. Dijkstra - https://www.cs.utexas.edu/~EWD/transcriptions/EWD03xx/EWD340.html * PHP release schedule problem - https://github.com/Danack/RfcCodex/blob/master/rfc_attitudes.md#not-being-compatible-with-the-php-release-schedule
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May 18, 2020 21:02 johannes@schlueters.de (Johannes =?ISO-8859-1?Q?Schl=FCter?=)
On Fri, 2020-05-15 at 12:53 +0100, Dan Ackroyd wrote:
> Obviously, all of the following is my own personal opinion, and other > people may have different opinions. > > There are two main lessons learnt from the SPL experience. > > i) Some APIs need to evolve separately from the PHP release > schedule*. > As otherwise any mistake in the design of the API is locked in until > the next minor release. > > ii) PHP needs a better way of installing extensions. There was a lot > of work done on this in https://github.com/FriendsOfPHP/pickle but > that effort seems to have been abandoned after a huge amount of work > was done for it. > > If anyone has any info on what the problems were with the approach > taken in that project, sharing that knowledge with the rest of the > PHP > community would be helpful in a new attempt to solve that problem.
I don't think this is the specific SPL learning. The goal of having many of those things in SPL (aside from helly having time and fun and doing things he liked) was that they were supposed to be the "Standard". Having one "observer" interface around everywhere. (picking that, since I never saw code using SPL's observer ...) Having it in a pecl module (even with a better tool) doesn't make them ubiquitous standards. The fact is that the internals group is a good group to discuss how the language itself should change, how the implementation should work. It however isn't good in defining APIs and interfaces. This is not only due to experience of the ones involved, but also since best practices evolve. What PHP provides is locked in the BC trap. Evolving it, changing it is hard. Luckily we are not in the times SPL was created, but 15 or so years later. We now have composer and a way smaller gap between C code and PHP userland for such things. It is now way simpler and way more approachable to put such things in userland packages and have other groups (like PSR process) design those. In the rare case where a design shows obvious benefits, but is slow one can consider putting it in C and then in the distribution, but we should aim to keep as many things in userland as we can. Actual users can simpler contribute their experience, it's simpler to debug, it's simpler to evolve/replace. APIs and interface in the implementation should be the basic foundation, as unopinionated as possible and enable to build "nice" interfaces in userland on top. Matching the framework of the week. For these things having a "simpler way" to install extensions isn't really critical. While rethinking PECL and its tooling is important! (what is it's role, it's function? Regarding code ownership, maintenance, hosting, being directory, offering [windows] build services, distribution, ...) If somebody were willing to think through all the related aspects and investing time on execution ... I'm happy to share my thoughts in more detail, while they have no proposed path, if somebody has the energy to drive it. Of course the line between what to put in C or userland is complicated. Let's take the iterators in SPL. A userland implementation will often have something like function next() { $this->innerIterator->next(); } in it. In userland code we need to do the function lookups each time. In the extension the lookup can be cached and the call can be sped up. With lots of iterator nesting and iterations over large collections this can be notable. If it warrants doing it in C one can discuss. (I haven't measured in PHP 7 days, but SPL contains pure PHP implementations of these things if somebody is intrigued) For archaeologists on PHP internals: This is the reason helly added the set of zend_call_method functions and macros in zend_interface.h allowing the cached lookups over the previous call_user_function() in zend_API.h. johannes
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May 18, 2020 22:10 internals@lists.php.net ("Levi Morrison via internals")
In my opinion, another key takeaway: inheritance as a code reuse
mechanism can really bite you. SplStack extends SplDoublyLinkedList
and this exposes a bunch of methods on a stack that don't make any
sense. It also means there are constraints on how well you can
optimize the stack, because you have these methods that don't make
sense on a stack that you _must_ support because some poor bloke
somewhere actually used them (may God have mercy on them).