Re: [RFC] Context Managers

On Tue, Nov 4, 2025, at 2:13 PM, Larry Garfield wrote: > Arnaud and I would like to present another RFC for consideration: > Context Managers. > > https://wiki.php.net/rfc/context-managers > > You'll probably note that is very similar to the recent proposal from > Tim and Seifeddine. Both proposals grew out of casual discussion > several months ago; I don't believe either team was aware that the > other was also actively working on such a proposal, so we now have two.. > C'est la vie. :-) > > Naturally, Arnaud and I feel that our approach is the better one. In > particular, as Arnaud noted in an earlier reply, __destruct() is > unreliable if timing matters. It also does not allow differentiating > between a success or failure exit condition, which for many use cases > is absolutely mandatory (as shown in the examples in the context > manager RFC). > > The Context Manager proposal is a near direct port of Python's > approach, which is generally very well thought-out. However, there are > a few open questions as listed in the RFC that we are seeking feedback > on. > > Discuss. :-) Hi all. I'm going to reply to several people at once in a single message, for simplicity: On Wed, Nov 5, 2025, at 12:29 AM, Paul Dragoonis wrote: > 1. Apart from wrapping zend_resource into ResourceContext, has there > been discussions or ideas to wrap other things ? Not really. The intent is that users can create their own "setup and teardown" logic packages and do with them as they please. Resources are just an oddball case in PHP, because reasons. I'm not sure what other auto-wrapping cases would make sense. That said, PHP could absolutely ship context managers for people to use explicitly. My ideal way to address async would be exactly that: The Scope example from the RFC, where the only way to get to a scope (and therefore start coroutines) is via a context manager, and PHP iself provides the scope types we want to support. Nothing else. There may be other managers that PHP would want to ship in the future for whatever reason, but that's out of scope for now. (No pun intended.) > 2. Are there any scenarios where using with() is a bad idea or has > "side effects"? If you have a setup/teardown routine that is only used once or twice, then making a context manager for just that one use case is likely overkill. Just write try/catch/finally as normal. I don't believe a context manager could handle this, although I've only rarely seen it in the wild: $success = true; try { // ... } catch (\Exception $e) { $success = false; } if ($success) { ... } (That is, leaking a variable from the setup/teardown code into the surrounding scope. Though, I suppose this would work in a pinch: $success = false; with (new Foo() as $f) { // ... $success = true; } if ($success) { ... } Not ideal, but would work. We're still exploring the possibility of making the context manager keyword an expression rather than a statement, which might offer other alternatives. Still brainstorming. > 3. In the implementation code there is a lot of mention of "list" and > zend_list .. why? Maybe the answer is obvious but I can't see, at first > glance, why we are implementing list under the hood. I will defer to Arnaud here. On Wed, Nov 5, 2025, at 12:45 AM, Valentin Udaltsov wrote: > Have you considered returning enum instead of ?bool? It would have a > clear self explanatory meaning. We have discussed that a bit, actually. The main concern is usability. The typical case will be to allow exceptions to propagate. If, say, a TypeError gets thrown 4 function calls down, you probably do want that to propagate to your top level handler, but still want to rollback your transaction or close your file or whatever. So the typical case should be easy, hence why we said null means the default behavior. And since null is falsy`, that fits neatly into a ?bool return; that is also what Python uses. With an enum, you'd have a much longer thing to type, plus it's less self-evident what no-return means. Ie, you'd have: function exitContext(?Exception $e): ContextResult { if ($e) { $this->conn->rollback(); // This line becomes required. return ContextResult::Propagate; } $this->conn->commit(); return ContextResult::Done; // Or, eh, what? } And not returning becomes a type error. Alternatively, we could assume null implies one of the other cases; but as shown above, there's still the issue that the return type is only meaningful in case of an exception, so it's unclear how that interacts. We're still open to discussion here. It also would play into the outstanding question of with as an expression. On Wed, Nov 5, 2025, at 1:38 AM, Deleu wrote: > Out of curiosity, what happens if GOTO is used inside a context block > to jump away from it? That would be a success case, just like break or return. Basically anything other than an exception is a success case. (That said, please don't use Goto. :-) ) > Could the RFC clarify the relation between Context and switch/case? I > thought it was really odd that something that triggers a warning on > switch/case is being introduced into a brand new language construct > basically creating the possibility for new code to fall into the same > trap as opposed to avoiding it in the first place. Specially a > construct like switch/case that has been in decline for over a decade > and ever since match came out on 8.0, switch case is practically > deprecated without actually being deprecated yet. What’s the > importance/relevance of being consistent with it? break and continue are interesting keywords. (In the "may you live in interesting times" sense.) Sometimes they have the same effect, if a control structure is non-looping. Or they may have different effects in case it is. The main non-looping case is switch, where for reasons that were before my time the decision was made to deprecate continue in favor of just supporting break. However, blocking it entirely is a problem, because that would change where continue 2 would go (as switch would be removed as a "level" that it could go to). It is kind of a mess. with is a non-looping control structure, and thus it seems logical to be consistent with other non-looping control structures. But, as noted, the other non-looping control structure is a mess. :-) Therefore, we get to choose between "a consistent mess" and "an inconsistent non-mess in one place and a mess in another." Neither is a fantastic option. We're open to both, depending on what the consensus is. > While we’re at it, do we really need break; statements inside context > blocks? If you want out you can: > > - return > - throw Both of those exit the function the with statement is in, which is not always desireable. > In the case of a nested block (break 2;) where I don’t want to wrap the > entire thing in try/catch, it seems like a GOTO out of it would be more > meaningful with text-based identifiers rather than number-based, which > leads to my first question (although I was more curious than actually > making an argument for it because I would rather avoid nested with as > much as possible). Because Goto was added to PHP as a troll, and not a feature you should actually use in production code 99.999% of the time. :-) On Wed, Nov 5, 2025, at 3:25 AM, Davey Shafik wrote: > I really like this RFC but have a couple of things to discuss: > > - automatically re-throwing exceptions: I think that this behavior, > especially with a boolean return value deciding if it happens or not is > not intuitive. I think a better approach is to do nothing with the > exception and let the user re-throw it if desired. I can't think of > anywhere else we re-throw exceptions unless the user indicates > otherwise. I'd rather leave the return value for return values; we > could expand this allow access to the return value like: with (foo() as > $foo return $bar) { }, and $bar would be set to null on void returns. Using the return value of exitContext() as the result of a "with expression" is something we are considering. However, we're modeling on Python (the most robust such functionality we are aware of), and they rethrow by default. Essentially, the concept is that exitContext() (and it's Python equivalent magic method), is mostly a finally block, not a catch block. finally blocks do propagate exceptions. In practice, many exitContext() methods will not need to differentiate; they'll just close a file or whatever and move on with life, which is why you would want an exception to propagate. The inclusion of the exception parameter makes it a sort of combined catch/finally, so it has some behavior of each. Another option we kicked around was splitting it into two methods; catchContext(Throwable $e) and exitContext(). However, that creates two other problems: 1. Because it's an interface, you would need to implement catchContext() all the time, even if you don't need it. That's very inconvenient. (Shamless plug for revisiting Levi's Interface Default Methods RFC, which would solve this issue: https://wiki.php.net/rfc/interface-default-methods) Using magic methods instead would avoid that problem, but then we're dealing with magic methods rather than a clearly-detectable interface. 2. If you need to run logic in both methods, do you duplicate it? Or worse, if you have logic that runs only on a success case, then what? Most likely you'd need to have your own $wasItAnError property inside the context manager object, which is ugly and annoying. That said, we're open to other ways to structure this logic. But I think in practice it's true that *most* use cases will want to propagate the exception, after doing appropriate local cleanup. > - context variable and scope: I know that you explicitly are not > creating a new scope, this means that the context variable will clash > with the enclosing scope namespace, and then the variable will be unset > after the context ends, this doesn't sit so well with me. I think I'd > rather see the same behavior as arrow function arguments, where it does > not override variables of the same name in the enclosing scope and > whatever value it has is lost at the end of the context, leaving the > outer scope version intact. Arnaud says that masking the context variable itself is probably fairly straightforward, so we can go ahead and do that. However, masking every variable that gets created doesn't make sense. This construct is not creating a new "block scope" in the language. It's just desugaring into a reusable try-catch-finally construct. If we wanted to have an actual local scope specific to the with block, then instead of the statement list we should have a callable, which in most cases would be an anon function. However, PHP's anon functions suck to use because of the need to explicitly use variables. That would effectively eliminate any benefit this feature offers, because you can already do $someWrapper->do($aCallable). But $aCallable needs a long list of use statements, which makes it fugly. If anon functions were fixed, that would make that approach easier to do.. However, that's been tried at least twice and it's been shot down both times, so I'm assuming we're stuck with a clunky anon function syntax indefinitely. ----- Also, off-list discussion has shown an interest in multiple context managers in one with block, which was one of the outstanding open questions. It looks like we'll probably include that, as it should be easy enough to do. ----- And now the big one... also in off-list discussion, Seifeddine noted that Laravel already defines a global function named with: https://github..com/laravel/framework/blob/12.x/src/Illuminate/Support/helpers.php#L510 And since this RFC would require with to be a semi-reserved keyword at the parser/token level, that creates a conflict. (This would be true even if it was namespaced, although Laravel is definitely Doing It Wrong(tm) by using an unnamespaced function.) Rendering all Laravel deployments incompatible with PHP 8.6 until it makes a breaking API change would be... not good for the ecosystem. So that means using Python's with keyword here is not going to work. Damn. A couple of other options have presented themselves, but we're open to other suggestions, too: 1. Java uses a parenthetical block on try for similar functionality (though without a separate context manager). That would look like: try (new Foo() as $foo) { // ... } // catch and finally become optional if there is a context. Pros here is that it introduces no new keywords, and context managers are effectively "packaged try-catch-finally" logic, so it fits. Downsides are that it gets more confusing now that try only sometimes requires a catch or finally. The ordering between the context manager and explicit catch/finally blocks is also non-obvious. It would also entirely preclude context blocks being an expression, as try is already non-expressional. 2. Either use or using. The semantics here would be identical to the current with proposal. Pros here are that use is already a reserved word, and using is, I hope, still available in practice. They could also be implemented as expressions if we figure out a way to do so. Downsides are that use is already used in a bunch of places to mean different things, so adding yet another contextual meaning just increases the complexity/confusion. using wouldn't have that issue, but we would still need to verify if it's available. --Larry Garfield