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Date: Sun, 09 Nov 2025 09:01:58 -0600
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Subject: Re: [PHP-DEV] [RFC] Context Managers
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From: larry@garfieldtech.com ("Larry Garfield")

On Sat, Nov 8, 2025, at 1:54 PM, Rowan Tommins [IMSoP] wrote:
> On 05/11/2025 22:38, Bob Weinand wrote:
>> The choice of adding the exception to the exitContext() is=20
>> interesting, but also very opinionated:
>>
>> - It means, that the only way to abort, in non-exceptional cases, is=20
>> to throw yourself an exception. And put a try/catch around the with()=20
>> {} block. Or manually use enterContext() & exitContext() - with a fak=
e=20
>> "new Exception" essentially.
>> - Maybe you want to hold a transaction, but just ensure that=20
>> everything gets executed together (i.e. atomicity), but not care abou=
t=20
>> whether everything actually went through (i.e. not force a rollback o=
n=20
>> exception). You'll now have to catch the exception, store it to a=20
>> variable, use break and check for the exception after the with block.=20
>> Or, yes, manually using enterContext() and exitContext().=20
>
>
> The Context Manager is *given knowledge of* the exception, but it's no=
t=20
> obliged to change its behaviour based on that knowledge. I don't think=20
> that makes the interface opinionated, it makes it extremely flexible.
>
> It means you *can* write this, which is impossible in a destructor:
>
> function exitContext(?Throwable $exception) {
>  =C2=A0 =C2=A0 if ( $exception =3D=3D=3D null ) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->commit();
>  =C2=A0 =C2=A0 } else {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->rollback();
>  =C2=A0 =C2=A0 }
> }
>
>
> But you could also write any of these, which are exactly the same as=20
> they would be in __destruct():
>
> // Rollback unless explicitly committed
> function exitContext(?Throwable $exception) {
>  =C2=A0 =C2=A0 if ( ! $this->isCommitted ) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->rollback();
>  =C2=A0 =C2=A0 }
> }
>
> // Expect explicit commit or rollback, but roll back as a safety net
> function exitContext(?Throwable $exception) {
>  =C2=A0 =C2=A0 if ( ! $this->isCommitted && ! $this->isRolledBack ) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->logger->warn('Transaction went out=
 of scope without=20
> explicit rollback, rolling back now.');
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->rollback();
>  =C2=A0 =C2=A0 }
> }
>
> // User can choose at any time which action will be taken on destruct =
/ exit
> function exitContext(?Throwable $exception) {
>  =C2=A0 =C2=A0 if ( $this->shouldCommitOnExit ) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->commit();
>  =C2=A0 =C2=A0 } else {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->rollback();
>  =C2=A0 =C2=A0 }
> }
>
>
> You could also combine different approaches, using the exception as an=20
> extra signal only if the user hasn't chosen explicitly:
>
> function exitContext(?Throwable $exception) {
>  =C2=A0 =C2=A0 if ($this->isCommitted || $this->isRolledBack) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 return;
>  =C2=A0 =C2=A0 }
>  =C2=A0 =C2=A0 if ( $exception =3D=3D=3D null ) {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->logger->debug('Implicit commit - c=
onsider calling=20
> commit() for clearer code.');
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->commit();
>  =C2=A0 =C2=A0 } else {
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->logger->debug('Implicit rollback -=
 consider calling=20
> rollback() for clearer code.');
>  =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this->rollback();
>  =C2=A0 =C2=A0 }
> }
>
>
> --=20
> Rowan Tommins
> [IMSoP]

Though one point to note here, $this->isCommitted on the context MANAGER=
 is not the same as isCommitted on the context VARIABLE.  So in the abov=
e examples you would have to either return $this from enterContext() (wh=
ich is fine), or save a reference to the context variable in the manager=
 and then check $this->txn->isCommitted (which is also fine).

Which you choose is mostly an implementation detail, and it's fine eithe=
r way; I just want to emphasize that a lot of the flexibility of context=
 managers comes from the separation of the context manager from the vari=
able.

A context manager is not just an auto-unsetter, though that is part of w=
hat it does.  It is more properly a way to abstract out and package up s=
etup/teardown lifecycle management, which can differentiate between a su=
ccess or failure case.  (At least as much as PHP itself is able to right=
 now.)  That has a wide variety of use cases, only a few of which a simp=
le destructor could handle. =20

--Larry Garfield