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Comment by 1ris | Hacker News Reader

Isn't Hack the PHP of the future, aviable today? For me it seems with hack there are no excuses anymore to still use php. I'd be glad if someone tell me some downsides of hack, it seems to good to be true. And how do the JITs compare?

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The problem I see is that Hack runs on HHVM rather than the standard PHP runtime, which is ubiquitous (some would argue that's its primary or only virtue).

So Facebook or any other company running code on their own server can shift to HHVM with (relative) ease but open source projects (like WordPress) and libraries can only switch once everyone else switches, Which leaves us in a catch-22, so Hack remains forever in a symbiotic/parasitic relationship with PHP.

you're probably interested in the downsides of HHVM, not Hack. Hack is really just a PHP frontend built on top of HHVM. HHVM is the JIT.

- it runs really well on expensive, FB hardware. there's no consideration given to anything else (performance-wise) in development. that's not to say it's slow, but it works best on 64GB servers with fat SSDs.

- it's a huge moving target when it comes to php5 compatibility -- there are a few intentional inconsistencies and a lot of unintentional ones. fixes for zend incompatibilities have a whack-a-mole effect: the typical patch fixes one inconsistency and introduces a few more.

- bad documentation and bad code quality

- it is open-source, but only in the most superficial sense. it's really an FB internal project, so good luck making any changes that help you but don't help FB

it's still better than zend PHP, and, to be fair, most of the incompatibilities are in cases where zend behaves stupidly. source: i was an HHVM contributor. (edited to space out my ascii list)

From the github page it looks like external folks are submitting pull requests. It looks like they require external people to sign the CLA, but it doesn't look like it's a case of "good luck making any changes that help you but don't help FB" per your comment.

I've found the same as you - people are getting their PRs when needed. In the earlier days of the project, it may have been true that they were less accepting of any non-critical changes (as they were still getting the core together), but in my experience they're open and eager to get feedback from the public.

my language was too harsh. see my edit in response to ptarjan.

I'm sorry to hear about your experience contributing to HHVM. Which commit(s) were you talking about? I'd rather stop doing whatever got in your way so others don't have the same experience.

really, the big problem was that the HHVM team didn't use CMake, so there was no concern with how long the build took and it was frequently broken. I had two instances where I spent hours fixing bugs that were fixed internally at FB at the same time, but hadn't been pushed. I know there was an ongoing effort to move completely into the open, but it was frustrating. I don't think these are persistent problems with HHVM, just reasons why the project wasn't really ready for primetime in the OSS world (open academy, specifically).

the fact that no one who doesn't work at FB is allowed to merge code (correct me if I'm wrong) made me feel like I was helping FB more than the OSS community. I get that HHVM is business critical to FB, but if you want it to truly get community support it needs to be spun off from FB.

edit: and I will add that my language was way too harsh. it's not hard to get in a PR provided it doesn't break anything in an FB internal test suite which I can't see (which never was a problem for me, but I could see it being one) and didn't degrade FB performance.

I half disagree with the third point - the documentation is certainly lacking (I recently used Redis on an HHVM site, and the adaptor had no documentation that it even existed; just read the source to figure it out), but it's a new-ish, fast-moving project, so that's not too surprising.

The code quality, however, isn't 'bad' by any stretch of the imagination. The FB team managing it is very knowledgeable about PHP internals, and are appropriately strict about determining what zend-compatibility fixes to commit. Their code's overall quite well-written, which makes me care a whole lot less about how poorly it's documented.

depends on what you define as good quality. it's efficient code, but it's sparsely commented, and a style nightmare.

Odd. If I recall correctly, there was even a detailed FB PHP coding style guide in the HHVM Git repo; that was afterwards removed though - I don't know why.

    sparsely commented

I already like the sound of it :)

Facebook moves fast. I'm not saying that they're going to abandon Hack or give it away to Apache or something, but if I were a corporation, sticking with vanilla PHP is attractive because it has a large developing body, and it's future isn't dependent on the whim of one company.

Otherwise, yeah, Hack is an improved PHP. To be clear, it adds additional functionality to PHP, but is still entirely backwards compatible. PHP >= 5.4 still has solid bones.

Hack also works really nicely with PHP - I think a lot of PMs hear about hack and think it's a workalike but completely separate language, not realizing that you can (and almost always will) have hacklang running alongside php. You're capable of declaring a class in hack (with strict-typing, method return types, better collection objects than just having 'Array' everywhere), with that class directly extending a PHP class.

80% of the reason I use hacklang is just so I can extend whatever base PHP classes my CMS provides, but implement my methods without having to add the piles of manual type-checking that PHP requires.

I've not tried this yet, though my boss has given me the go-ahead. What editor do you use to find out how it's going? I struggle a little bit with it because I'm yet to vim-hack running. Do you just stick to the "code save refresh" cycle? Does Hack give you type checking error messages in the web page? Can you run a "check types" command on code from the terminal?

Statically typed usually means the compiler checks types during compilation and throws away information about them after generating the target code (usually, there are exceptions like Java). So I doubt it will be able to tell you anything about types in the ouput (the web page) unless you do something with runtime contracts.

Hack doesn't get compiled, heh, it's interpreted so it's quite a bit different to what I'm used to. It's more like TypeScript in that regard, but TypeScript is still compiled... I've never used an interpreted typed language before, hence the question!

Well HHVM is a JIT compiler isn't it? Also it applies just as well to an intermediate representation (like bytecode, or some simpler language that gets evaluated).

HHVM enforces the checks purely dynamically as it actually executes code. There's a totally separate tool that does the full static type analysis. See my sibling comment for details: https://news.ycombinator.com/item?id=7808586

> there are exceptions like Java

Actually Java works in the same way; the confusion stems from imprecise use of jargon. Java tends to use the word "type" for things which would more precisely be called "tags". Tags are the run-time information which distinguish different values of the same type, and can't be erased in general.

Java adds a bunch of rules about handling tags, for example object values have a "class" tag; class tags must be statically specified (AKA "type signatures"); class tags can be pattern-matched automatically (AKA dynamic dispatch, method overloading and inheritance), allowing functions to be defined in separate chunks (AKA methods); functions can only be applied to arguments which will match a pattern (AKA "type checking"), etc.

These rules are checked at compile time as well as the types. Unfortunately all these different concepts tend to be grouped under the umbrella term "type checking", which makes fine-grained discussion and comparisons to other languages more difficult.

Unfortunately the only way to get type errors statically right now is to run `hh_client` at the command line (see http://docs.hhvm.com/manual/en/install.hack.bootstrapping.ph...) -- this is what vim-hack will do for you. HHVM will only report type errors that it can see at runtime, which won't catch the edge cases or error cases you didn't think to test, which kind of defeats the purpose of having the static type system. For a really simple integration, you can do `watch hh_client` in a second window, which will run the checker every 3 seconds, configurable, see `man watch`.

This separation is different than many other languages, and lots of folks have found it confusing. It largely exists for technical reasons, and we should be able to have a better UX for end users; this is something I've been thinking a lot about and want to try to improve in the language going forward. (I work full-time on the Hack team.) Please do give it a shot and let us know how it goes!

Funny, I was in the IRC channel this evening having a chat to Simon and managed to work all this out! I'm actually quite excited by it, I think the type checking that's available + unit testing will catch most of the edge cases I was looking to catch, although that "doesn't check global scope" threw me for a bit when getting it all up and running!

I'm really interested to see what you end up coming up with UX wise. What sort of edge cases do you think the `hh_*` apps will miss? Running `hh_client` on save isn't a bad thing, IMO, and having it output JSON for easy integration is amazing :) But I'm curious what the type checker will miss currently?

Is there a public mailing list where these sorts of discussions happen or is it more internal to Facebook? I'm really interested in Hack (as is where I work, we push PHP to it's limits so we're keen to use something that can catch even more bugs from day 0) so thanks very much for pushing PHP even further forward!

Are the technical reasons for missing type errors that wouldn't be triggered at run-time insurmountable? Or is it more a "finding the right UX to expose it"?

It's not that the tyepchecker will miss things, it's that, for folks coming from other languages, it's not clear that there even exists a separate typechecker you have to run!

There isn't a mailing list right now. A few discussions are just in-person since we sit next to each other, but we're trying to make things as transparent as we can. Lots of stuff (and hopefully more moving forward) happen on #hhvm on Freenode or on GitHub issues -- basically the same channels as the HHVM project itself. There is also nontrivial discussion during code review, which is very unfortunately all internal right now; we hope to have that all moved external as soon as we can. (There are a lot of tricky integrations with internal tools that need to happen for that to work.)

I guess hack is not backward compatible with some older php code. Particularly code that mingles php and html together. For a lot of us this doesn't matter (frameworks and templating engines), but a lot of tutorials mix the html and php.

Most frameworks work with hack now, so your right it would be easier if there where just 1 version of "php".

Hack has incompatibilities with some current PHP code too. Particularly the different syntax for generators (PHP 5.5) and the upcoming syntax for variadic functions (PHP 5.6).

Can you elaborate on these incompatibilities, particularly generators? I work on the project and the only generator incompatibility I know of is that what PHP5 calls "Generator" we call "Continuation", but only since we haven't gotten around to renaming ours yet :) I'm also pretty sure HHVM supports 5.6 variadic functions in PHP code, or will very soon; the Hack typechecker currently does not, but that is strictly a missing feature, and something we do want to support.

There's already open issues in GitHub regarding the differences in generator syntax -- I commented in one:

https://github.com/facebook/hhvm/issues/1787

I guess the class has been renamed in trunk, but according to this, the syntax differences still remain:

https://github.com/facebook/hhvm/issues/1871

And while we're at it, might as well point out the missing Closure::bind and Closure::bindTo from PHP 5.4:

https://github.com/facebook/hhvm/issues/1203

Hack is nice. But right now is only backed by Facebook. PHP is backed by a bigger community.

Hack's backed by its own open-source community too, and in its own way, is also backed by the PHP community. Laravel, symfony, cakephp, doctrine, etc. are often run on HHVM and support hacklang applications. What makes PHP better makes hack better, and hack has a growing community of developers making hack better too.

Sure, if you only want to run code on 64-bit linux.

That does not sound like a very burdensome limitation for serious PHP applications.

PHP isn't just for the big iron in the sky. I've used it for a web portal on networking equipment and it was a perfect fit.

Whatever the future is, it will most likely have ports available in most platforms.

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