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Date: Tue, 01 Oct 2024 20:06:07 +0100
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Subject: Re: [PHP-DEV] Protected destructors
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On Tue, 1 Oct 2024, at 19:29, Larry Garfield wrote:
> I would have said with() would be neat in PHP. :-)

I have been considering for a while proposing Context Managers [Python's with(), not to be confused with VisualBasic & JavaScript unrelated feature with the same keyword].

My primary example use case is safe database transactions, which I've seen implemented in PHP in two ways:

1) Callback style, where the code to run in a transaction has to be wrapped in a function, usually an anonymous closure. This is often cited as a use case for implicit capture in closures, but even with that it adds a layer of indirection, and changes the meaning of "return" and "yield" inside the wrapped block.

2) "Resource Acquisition Is Initialization" style, where the destructor rolls back the transaction if it hasn't been committed or rolled back manually. This requires fewer changes to the wrapped code, but as Arnaud points out, it's not 100% reliable / predictable in PHP, due to details of the GC.

Context Managers present a third option, where the code in the transaction remains a normal sequence of statements, but there is a more explicit guarantee about what will happen when the with{} block is exited. The Python design document has interesting background on what they included and excluded: https://peps.python.org/pep-0343/

C#'s "using statement" is similar, but explicitly designed for ensuring the correct "disposal" of an object rather than hooking entry to and exit from a "context": https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/using

Regards,
-- 
Rowan Tommins
[IMSoP]