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Mon, 19 Jan 2026 13:10:45 -0500 (EST) Content-Type: multipart/alternative; boundary="------------lcL0HfyFzmPucVqfPopI8D9Q" Message-ID: <44015fee-b20c-4018-8b77-49955aeb4c31@rwec.co.uk> Date: Mon, 19 Jan 2026 18:10:43 +0000 Precedence: list list-help: list-unsubscribe: list-post: List-Id: x-ms-reactions: disallow MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PHP-DEV] [RFC] Context Managers To: internals@lists.php.net References: Content-Language: en-GB In-Reply-To: From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]") This is a multi-part message in MIME format. --------------lcL0HfyFzmPucVqfPopI8D9Q Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 19/01/2026 15:58, Larry Garfield wrote: > In an ideal world, if we had auto-capturing long-closures, then I would agree this is largely unnecessary and could instead be implemented like so (to reuse the examples from the RFC): > > $conn->inTransaction(function () { > // SQL stuff. > }); > > ... > > If we had auto-capturing closures, I would probably argue that is a better approach. I haven't caught up with the discussion fully, but I want to pick up on this specifically, because I disagree. Inversion of control like this would only be suitable in the general case if we had auto-capture *by reference*. I believe every proposal so far has limited automatic capture to *values only*. Auto-capture by value helps you get values *into* the closure, but does not help get anything back *out*. So, if the code you want to sugar looks like this: ``` try{ $db->beginTransaction(); // ... $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId'); $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId'); // ... $db->commitTransaction(); } finally{ if( $db->isInTransaction()) { $db->rollbackTransaction(); } } // use $newFooId and $newBarId here ``` Then your options with a capture-by-value closure are either a) list the outputs as manual by-ref captures: ``` $newFooId = $newBarId = null; $db->inTransaction(fn() use (&$newFooId, &$newBarId) { // ... $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId'); $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId'); // ... }); // use $newFooId and $newBarId here ``` or b) return the outputs, and extract them using array destructuring or similar: ``` [$newFooId, $newBarId] = $db->inTransaction(fn() { // ... $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId'); $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId'); // ... return [$newFooId, $newBarId]; });// use $newFooId and $newBarId here ``` A Context Manager - or any other syntax based on a code block rather than a full stack frame - instead gives you direct access to the local variables: ``` using($db->transaction()) { // ... $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId'); $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId'); // ... }// use $newFooId and $newBarId here ``` Even if we had automatic capture by value, I think Context Managers would be a useful proposal to discuss. -- Rowan Tommins [IMSoP] --------------lcL0HfyFzmPucVqfPopI8D9Q Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit
On 19/01/2026 15:58, Larry Garfield wrote:
In an ideal world, if we had auto-capturing long-closures, then I would agree this is largely unnecessary and could instead be implemented like so (to reuse the examples from the RFC):

$conn->inTransaction(function () {
  // SQL stuff.
});

...

If we had auto-capturing closures, I would probably argue that is a better approach.


I haven't caught up with the discussion fully, but I want to pick up on this specifically, because I disagree.

Inversion of control like this would only be suitable in the general case if we had auto-capture *by reference*. I believe every proposal so far has limited automatic capture to *values only*.

Auto-capture by value helps you get values *into* the closure, but does not help get anything back *out*.

So, if the code you want to sugar looks like this:

```
try {
    $db->beginTransaction();
    // ...
    $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId');
    $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId');
    // ...
    $db->commitTransaction();
}
finally {
    if ( $db->isInTransaction() ) {
        $db->rollbackTransaction();
    }
}
// use $newFooId and $newBarId here
```


Then your options with a capture-by-value closure are either

a) list the outputs as manual by-ref captures:

```
$newFooId = $newBarId = null;
$db->inTransaction(fn() use (&$newFooId, &$newBarId) {
    // ...
    $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId');
    $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId');
    // ...
});
// use $newFooId and $newBarId here
```


or b) return the outputs, and extract them using array destructuring or similar:

```
[$newFooId, $newBarId] = $db->inTransaction(fn() {
    // ...
    $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId');
    $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId');
    // ...
    return [$newFooId, $newBarId];
});
// use $newFooId and $newBarId here
```


A Context Manager - or any other syntax based on a code block rather than a full stack frame - instead gives you direct access to the local variables:

```
using($db->transaction()) {
    // ...
    $newFooId = $db->execute('INSERT INTO Foo ... RETURNING FooId');
    $newBarId = $db->execute('INSERT INTO Foo ... RETURNING BarId');
    // ...
}
// use $newFooId and $newBarId here
```


Even if we had automatic capture by value, I think Context Managers would be a useful proposal to discuss.


-- 
Rowan Tommins
[IMSoP]
--------------lcL0HfyFzmPucVqfPopI8D9Q--