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Date: Thu, 24 Oct 2019 13:47:08 +0100
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To: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Re: [RFC] Union Types v2
From: rowan.collins@gmail.com (Rowan Tommins)

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Hi Dmitry,

On Wed, 23 Oct 2019 at 16:43, Dmitry Stogov <dmitry@zend.com> wrote:

> Actually, I think PHP already took wrong direction implementing "typed
> references" and "type variance".
> Introducing more "typing", we suggest using it, but this "typing" comes
> with a huge cost of run-time checks.
> From 10% (scalar type hint of argument) to 3 times (typed reference
> assignment) performance degradation.
> Anyone may rerun my benchmarks
> https://gist.github.com/dstogov/fb32023e8dd55e58312ae0e5029556a9
>


I think this performance impact is a real concern; PHP is the only language
I know of which implements type checks entirely at run-time in production
code, and we should ask ourselves if that's definitely the right approach.

Would it be possible, at least in principle, to build a static analysis
tool which could prove that certain type checks would never fail, and prime
OpCache with code that leaves them out? As I understand it, this is how
Dart works: the compiler only emits run-time checks for assertions it can't
prove true by static analysis.

The simpler idea I had in this area was caching what type checks a value
had passed, either on each zval or perhaps just at the class level, so that
checking the same type again would be much faster, even if it was a complex
union with multiple interfaces.

Regards,
-- 
Rowan Tommins
[IMSoP]

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