Re: Examples comparing Block Scoped RAII and Context Managers

From: Date: Thu, 27 Nov 2025 09:08:14 +0000
Subject: Re: Examples comparing Block Scoped RAII and Context Managers
References: 1 2 3  Groups: php.internals 
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Hi

Am 2025-11-19 23:19, schrieb Rowan Tommins [IMSoP]:

On 18/11/2025 17:23, Larry Garfield wrote:

One thing I definitely do not like is the need for a FileWrapper class in the RAII file-handle example.  That seems like an unnecessary level of abstraction just to squeeze the fclose() value onto the file handle.  The fully-separated Context Manager seems a more flexible approach.



Yes, exploring how exactly that flexibility could be used was part of my motivation for the examples I picked.

The downside is that it is slightly harder to understand at first glance: someone reading "using (file_for_write('file.txt') as $fh)" might well assume that $fh is the value returned from "file_for_write('file.txt')", rather than the value returned from "file_for_write('file.txt')->enterContext()".

What made sense to me was comparing to an Iterator that only goes around once - in "foreach (files_to_write_to() as $fh)", the "files_to_write_to()" call doesn't return $fh either, "files_to_write_to()->current()" does.


For me the relevant keyword that indicates that the value is not used directly is not the 'as', but the 'each' part of the 'foreach'. Just by reading it as a English sentence, it becomes clear to me what is happening.

The same is not true for me for `using (file_for_write('file.txt') as $fh) or even worse using (new Manager() as $notActuallyTheManager)` (which is part of the RFC). AFAICT the latter is not so much a problem in Python, because there is no difference between constructors and factory functions and also because there is no actual type declaration. This means open() could be a function returning a file handle or it could be the “constructor“ for a context manager (that then returns the file handle as part of entering the context) and the difference is effectively indistinguishable from the outside, which is not the case in PHP.

Best regards
Tim Düsterhus

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