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Date: Wed, 5 Nov 2025 23:27:41 +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 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.

It also means you can trivially wrap values that have no idea about 
context managers, without needing a load of extra proxy code; it's why 
the RFC can include implicit handling for resources; and why the 
generator example in the Future Scope section works.


-- 
Rowan Tommins
[IMSoP]