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Date: Sat, 15 Nov 2025 23:11:44 +0000
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Subject: [PHP-DEV] Examples comparing Block Scoped RAII and Context Managers
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

Hi all,

The Block Scoping RFC and the Context Manager RFC cover a lot of similar 
use cases, and a lot of the discussion on both threads has been 
explicitly comparing them.

To try to picture better how they compare, I have put together a set of 
examples that implement the same code using both features, as well as 
some other variations, in this git repo: https://gitlab.com/imsop/raii-vs-cm

A few notes:

- The syntax for the two proposals is based on the current RFC text. If 
they are updated, e.g. to use different keywords, I will update the 
examples.

- I have included examples with closures which automatically capture by 
value, since a lot of the same use cases come up when discussing those.

- There are many scenarios which could be included, and many ways each 
example could be written. I have chosen scenarios to illustrate certain 
strengths and weaknesses, but tried to fairly represent a "good" use of 
each feature. However, I welcome feedback about unintentional bias in my 
choices.

- Corrections and additional examples are welcome as Merge Requests to 
the repo, or replies here.


With that out of the way, here are my own initial thoughts from working 
through the examples:

- RAII + block scope is most convenient when protecting an existing 
object which can be edited or extended.

- When protecting a final object, or a native resource, RAII is harder 
to implement. In these cases, the separation of Context Manager from 
managed value is powerful.

- Context Managers are very concise for safely setting and resetting 
global state. RAII can achieve this, but feels less natural.

- An "inversion of control" approach (passing in a callback with the 
body of the protected block) requires capturing all variables *not* 
scoped to the block. Even with automatic by-value capture, those needed 
*after* the block would need to be listed for capture by reference.

- Building a Context Manager from a Generator can lead to very readable 
code in some cases, and closely mimics an "inversion of control" 
approach without the same variable capture problems.


I would be interested in other people's thoughts.

Regards,

-- 
Rowan Tommins
[IMSoP]