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To: Rasmus Lerdorf <rasmus@lerdorf.com>
CC: Anthony Ferrara <ircmaxell@gmail.com>,
        Larry Garfield
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Thread-Topic: [PHP-DEV] Reviving scalar type hints
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Date: Fri, 20 Feb 2015 18:52:39 +0000
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Subject: Re: [PHP-DEV] Reviving scalar type hints
From: jwatzman@fb.com (Josh Watzman)

On Feb 20, 2015, at 10:30 AM, Rasmus Lerdorf <rasmus@lerdorf.com> wrote:

> On 02/20/2015 09:39 AM, Anthony Ferrara wrote:
>> I think if anything, the appearance of Hack (and its adoption) show
>> that people want static typing, at least to some level...
>=20
> To be perfectly transparent here though, you should mention that your
> proposed RFC goes well beyond the strict typing that is in Hack because
> in Hack the internal API is largely untyped while your proposal is to
> default the entire internal API to strict types in strict mode. Also, in
> Hack there is a distinction between the off-line hh_client type-checker
> and the runtime.

This distinction is going away pretty soon. The typechecker is an integral =
part of Hack, and you shouldn't be able to ignore its errors. The runtime w=
ill soon consider them fatal errors too. If your code doesn't pass the hh_c=
lient typechecker, then its behavior when run on HHVM is completely undefin=
ed.

> Hack examples all using <?hh // strict
>=20
>  echo number_format('1000');
>  echo htmlspecialchars(1000);
>  echo md5(1000);
>=20
> These are all fine both as far as the type-checker is concerned as well
> as the runtime, of course, but they are runtime fatals in your proposed R=
FC.\

And they should be errors in Hack too. The reason they aren't are to ease t=
ransitions from PHP to Hack. I'd expect them to be more strongly typed even=
tually.

> And if you only go by the runtime and ignore the out-of-band type
> checker there are almost no strictness rules applied to the internal API
> in Hack.
>=20
> eg.  explode(0, 1000);
>=20
> Here the hh_client type checker will complain that it is expecting
> strings, but the runtime will run it nicely.
>=20
> So when you say, and as I have heard other people say, that people want
> Hack-like strict typing, you have to be a bit careful about what is
> meant by that. Even in the cases where the internal API is typed in
> Hack, it is still not a runtime fatal if they are called with the wrong
> types.

See above -- relying on (or even really thinking about) this distinction is=
 relying on implementation details which are going to change.

Josh