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Date: Sun, 15 Mar 2020 20:03:53 +0000
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Subject: Re: [PHP-DEV] RFC idea: Block scoped variables with "let $x = expr"
From: rowan.collins@gmail.com (Rowan Tommins)

On 15/03/2020 18:17, tyson andre wrote:
> If this feature freed variables when going out of scope,
> it would be compiled more like the following (if there were multiple lets):
>
> JavaScript doesn't have destructors, but PHP does, which makes the implementation a tiny bit more complex.
>
> ```
> try {
>      $x = new Foo();
>      $otherLet = new Other();
>      $x->bar();
> } finally {
>      // try/finally is useful if unset($otherLet) could throw from __destruct
>      try {
>          unset($otherLet);
>      } finally {
>          unset($x);
>      }
> }
> somethingElse();
> ```


I'm still not 100% clear why all this would be necessary. Do you know 
how the equivalent code works with function-scoped variables? As far as 
I can see, returning from a function will successfully call multiple 
destructors even if one of them throws an exception. Could exiting block 
scope use that same algorithm?

Having the variable become inaccessible but not actually deallocated 
seems like it would cause a lot of confusion.

For instance:

{
     let $fh1 = fopen('/tmp/foo', 'wb');
     flock($fh1);
     fwrite($fh1, 'Hello World');
     // no fclose(), but $fh1 has fallen out of scope, which would 
normally close it
}
{
     let $fh2 = fopen('/tmp/foo', 'wb');
     flock($fh2, LOCK_EX); // won't obtain lock, because $fh1 is still 
open, but no longer accessible
}

Regards,

-- 
Rowan Tommins (né Collins)
[IMSoP]