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Date: Sat, 17 Jun 2023 15:59:04 +0100
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Subject: Re: [PHP-DEV] Expression code blocks
From: rowan.collins@gmail.com (Rowan Tommins)

On 17/06/2023 12:26, Ilija Tovilo wrote:
> I don't believe blocks for general expressions are that useful in PHP
> due to the lack of block scoping. Your suggestion to make the block a
> separate closure could avoid that (as well as the optimizer issue
> mentioned below) but comes with new issues, like making modification
> of captured values impossible without by-ref capturing.


I've been pondering various things in this space for a while, 
particularly since the last auto-capture closures RFC. I haven't quite 
coalesced on a coherent concept, but there are a few things that I think 
inter-relate:

* Opting into block-scoped variables, while retaining full access to the 
outer scope, like JS "let"
* Code blocks as some kind of first-class thing, distinct from closures
* Macro-like constructs that take a block of code and do something 
special with it, or something like Python's "context managers"

One of the use cases people often cite for auto-capture in closures is 
for use in patterns like this:

$db->doInTransaction(function() use (...) {
     $db->execute('some SQL here');
     $db->execute('some more SQL');
     // etc
});

Or this:

$name = $cache->memoize(function() use (...) {
     $result = $db->query('some SQL');
     return $result['item_name'];
});

This is a nice pattern, but closures are quite a heavy tool for this 
job, requiring two extra stack frames (the doInTransaction or memoize 
method, and the closure itself), and boilerplate to pass the result back 
through.

As I say, I haven't got a coherent design, but I think it would be great 
to have something context-manager-like:

$name = with($cache->memoize() as $cacheItem) {
     let $result = $db->query('some SQL');
     $cacheItem->save( $result['item_name'] );
} );

... or macro-based:

$name = null;
$cache->memoize!($name, block {
     let $result = $db->query('some SQL');
     $name = $result['item_name'];
} );


Regards,

-- 
Rowan Tommins
[IMSoP]