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Date: Wed, 20 Apr 2016 11:50:39 +0200
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Subject: Re: [PHP-DEV] Re: Improving PHP's type system
From: johannes@schlueters.de (Johannes =?ISO-8859-1?Q?Schl=FCter?=)

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On Wed, 2016-04-20 at 18:32 +1000, Jesse Schalken wrote:
> On Thu, Apr 14, 2016 at 10:47 PM, Lin Yo-An <cornelius.howl@gmail.com>
> wrote:
>=20
> >
> > I think the original purpose of adding type system in Hack, is to provi=
de
> > just-in-time compilation, this provides more information to let compile=
r to
> > optimize the code with specific type.
> >
> >
> Last I checked, the HHVM JIT treats PHP and Hack code roughly identically
> and doesn't use the Hack type annotations for any optimisation. It's is
> really just another dynamic language JIT, like V8 and Chakra.
>=20
> The purpose of type annotations and type checkers for dynamic languages,
> including Hack, TypeScript and Flow, is not necessarily to improve
> performance but to improve developer efficiency. Wherever there exists a
> type annotation which is enforced, either statically or at runtime, the
> developer has gained important knowledge to inform the modification of th=
e
> program, and can do so with increased certainty and predictability.

For that there is some research:

        How many bugs does static type checking catch?
        [...]
        answer: 2%.
        [...]
        not only were development times significantly shorter on average
        with dynamically typed languages, so were debug times.
       =20
        So all those nasty type errors were actually not having any
        negative impact on debug times, in fact the reverse was true.
       =20
        http://blog.metaobject.com/2014/06/the-safyness-of-static-typing.ht=
ml

johannes

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