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Date: Mon, 23 Feb 2015 15:15:26 +0100
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Subject: AW: [PHP-DEV] JIT (was RE: [PHP-DEV] Coercive Scalar Type Hints RFC)
From: php@tutteli.ch ("Robert Stoll")

Heya Anthony,

> -----Urspr=C3=BCngliche Nachricht-----
> Von: Anthony Ferrara [mailto:ircmaxell@gmail.com]
> Gesendet: Montag, 23. Februar 2015 14:53
> An: Robert Stoll
> Cc: PHP internals
> Betreff: Re: [PHP-DEV] JIT (was RE: [PHP-DEV] Coercive Scalar Type =
Hints RFC)
>=20
> Robert,
>=20
> On Mon, Feb 23, 2015 at 3:27 AM, Robert Stoll <php@tutteli.ch> wrote:
> > Hey all,
> >
> > tl;dr
> >
> > Just one point which JIT/AOT people should consider when dealing =
with PHP. PHP is highly dynamic and there are enough
> use cases which makes it impossible for a static analyser to infer =
types accurately without using a top type like mixed.
> > How would you deal with variable function calls, variable variables, =
reflection, dynamic includes etc.
> >
> > Your inferred types would simply be wrong without using mixed.
> > Consider the following
> >
> > function foo(int $a){}
> > $a =3D 1;  //can be int for sure right?
> > $b =3D "a";
> > $$b =3D "h"; //oh no, your generated code would crash foo($a);
> >
> > Maybe I am wrong and there is a possibility, if so, please let me =
know, would be interesting to know.
>=20
> This very specific example is easy to type. The reason is that we can =
use constant propagation to know that $$b is really $a
> at compile time. Hence we can reduce it to:
>=20
> $a =3D "h";
> foo($a);

[Robert Stoll]=20
Sure, "a" was just an example to illustrate the problem. I figured it =
would not be necessary to say that the value of $b can be completely =
unknown by the static analyser -> could come from user input, from a =
database, from unserialising code etc. (but probably that is what you =
meant with "this isn't the general case" below).

Assuming statically that $a is int or $b is string is erroneous in this =
context.

Another problem to illustrate that a top type or at least some form of =
union type is required:

function foo($x, $y, $z){
  $a =3D 1;
  if($x){
    $a =3D "1";
  }
  If($y > 10){
    $a =3D [];
  }
  If($z->foo() < 100){
    $a =3D new Exception();
  }
  echo $a;
  return $a;
}

How do you want to type $a without using a union type?

>=20
> And hence know **at compile time** that's an error.
>=20
> This isn't the general case, but we can error in that case (from a =
static analysis perspective at least) and say "this code is too
> dynamic". In strict mode at least.

[Robert Stoll]=20
If you go and implement a more conservative type system than the actual =
dynamic type system of PHP well then... you can do whatever you want of =
course.
But if you do not just want to support just a limited set of PHP then =
you will need to include dynamic checks in many places. Or do you think =
that is not true?


> Anthony