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Date: Thu, 06 Nov 2025 12:18:26 +0000
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Subject: Re: [PHP-DEV] [RFC] Context Managers
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On 5 November 2025 23:58:52 GMT, Bob Weinand <bobwei9@hotmail=2Ecom> wrote:

>However, I still think the proposed approach is dangerous with respect to=
 forgetting the exitContext() call=2E When using manual handling=2E But yes=
, I agree, that's a much more manageable concern=2E
>And the onus of handling duplicate enterContext() and multiple exitContex=
t() calls still lies on the implementer=2E The RFC does zero effort at addr=
essing this=2E

I think the relationship to Iterators is significant: if you put an iterat=
or in a variable, it's perfectly possible to use it in two different foreac=
h statements, or manually call the interface methods, and get very confusin=
g results=2E

But most of the time, you don't take a reference to the iterator at all, a=
nd the same would be true of Context Managers:

foreach ( $foo->iterate() as $item ) { =2E=2E=2E }
with ( $foo->guard() as $resource ) { =2E=2E=2E }


That said, it seems like it would be easy enough to add a mandatory state =
check - a boolean property on the interface, and a check in the de-sugared =
code:

if ( ! $__mgr->canEnter ) { throw SomeError; }
$__mgr->canEnter =3D false;=20

That would also give the implementation a choice of whether to reset it on=
 exit, or make the object strictly single use=2E


That doesn't stop you manually calling the enterContext and exitContext me=
thods in unintended ways, but that's actually true of RAII or Disposable de=
signs, at least in PHP: there's nothing stopping you calling __construct or=
 __destruct as normal methods, and causing all sorts of unintended behaviou=
r=2E




Rowan Tommins
[IMSoP]