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Date: Thu, 6 Nov 2025 00:58:52 +0100
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Subject: Re: [PHP-DEV] [RFC] Context Managers
To: "Rowan Tommins [IMSoP]" <imsop.php@rwec.co.uk>, internals@lists.php.net
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From: bobwei9@hotmail.com (Bob Weinand)

Hey Rowan,

On 6.11.2025 00:27:41, Rowan Tommins [IMSoP] wrote:
> On 05/11/2025 22:38, Bob Weinand wrote:
>> I don't like that design, which effectively forces you to put safety 
>> checks for all but the simplest cases onto the ContextManager 
>> implementation.
>> And it forces the user to recognize "this returned object 
>> DatabaseTranscation actually implements ContextManager, thus I should 
>> put it into with() and not immediately call methods on it". (A 
>> problem which the use() proposal from Tim does not have by design.) 
>
>
> I think you may have missed the key distinction between a "Context 
> Manager" (as designed by Python) and a "Disposable" (as used in C# and 
> others): the Context Manager is not the resource itself, it exists 
> only to meet the protocol/interface.
>
> In this code:
>
> with ( $dbConnection->transaction() as $handle ) {
>    $handle->execute('I am in the transaction');
> }
>
> $handle is *not* the value returned by $dbConnection->transaction(), 
> it's the value returned by $dbConnection->transaction()->enterContext().
>
>
> One of the things that means is that if you just write 
> $foo=$dbConnection->transaction() you can't accidentally run any 
> methods on $foo, if all it has is enterContext and exitContext. 


You are right, I missed that there's an extra layer of nesting inside this.
I think the DatabaseTransaction example put me on the wrong thought path 
because it just returned the connection it came from instead of a 
dedicated nested Transaction object. (The enterContext method in that 
example ought to include a startTransaction call.)

However, I still think the proposed approach is dangerous with respect 
to forgetting the exitContext() call. When using manual handling. But 
yes, I agree, that's a much more manageable concern.
And the onus of handling duplicate enterContext() and multiple 
exitContext() calls still lies on the implementer. The RFC does zero 
effort at addressing this.

Thanks,
Bob