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]
