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To: Rowan Tommins <rowan.collins@gmail.com>, "internals@lists.php.net"
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Thread-Topic: [PHP-DEV] Autoloading functions/consts without a performance
 impact
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Date: Sun, 5 Jan 2020 18:03:08 +0000
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Subject: Re: [PHP-DEV] Autoloading functions/consts without a performance
 impact
From: tysonandre775@hotmail.com (tyson andre)

> Yes, I'm saying that the autoloader should be called for each lookup, so=
=0A=
> autoloading of Foo\strlen should come between checking if Foo\strlen is=
=0A=
> defined, and checking if \strlen is defined.=0A=
=0A=
That would be the intuitive approach for a language,=0A=
but as mentioned earlier,=0A=
it would significantly harm performance of existing code for php 7=0A=
(slightly without an autoloader, more with autoloaders),=0A=
and I can't imagine that getting approved.=0A=
=0A=
- One option I'd thought of is to invalidate runtime caches of=0A=
  ambiguous calls' opcodes when the set of autoloaders change.=0A=
  This is technically possible,=0A=
  but it would make spl_autoload_register()/spl_autoload_unregister() extre=
mely slow for large applications.=0A=
  (it would be implemented by iterating over all functions/closures/methods=
/global scopes=0A=
  and deleting the runtime cache entry for those call opcodes.)=0A=
=0A=
  That way, if a new autoloader got registered, existing unqualified calls =
to strlen()=0A=
  would check for \Foo\strlen once, the next time they were called.=0A=
=0A=
  I don't have any plans to try this or work on this approach,=0A=
  but it's worth noting that it's possible.=0A=
  This approach is taken in http://github.com/runkit7/runkit7=0A=
  when modifying definitions of internal functions (runkit_function_redefin=
e()), etc.=0A=
=0A=
> Then maybe we should target the feature at those use cases - don't call t=
he=0A=
> autoloader *at all* unless we know the fully-qualified name, and give up=
=0A=
> trying to "square the circle" by combining fallbacks with autoloading for=
=0A=
> unqualified names?=0A=
=0A=
The largest issue with that is that unqualified names are extremely common =
in php 7 code.=0A=
=0A=
I'd considered that option, but that introduces its own surprises,=0A=
which I'd consider to have more frequent and significant impact on applicat=
ions that start using this.=0A=
=0A=
namespace NS;=0A=
function f1($x) {=0A=
     return mb_strlen($x) + 1;=0A=
}=0A=
function f2($x) {=0A=
     return \mb_strlen($x) * 2;=0A=
}=0A=
=0A=
Calling f2() then f1() would work, but f1() then f2() would not work, becau=
se f1() wouldn't autoload.=0A=
=0A=
- ASIDE: I guess something along these lines would be less likely to *cause=
 surprises*=0A=
  if one implemented "autoload, but only for qualified functions outside of=
 the global namespace,=0A=
  but autoloading global functions is my main reason to want this with curr=
ent code (e.g. polyfills).=