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Date: Fri, 26 Jan 2018 08:20:31 -0600
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To: Niklas Keller <me@kelunik.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV][RFC][DISCUSSION] Collection Inspection
From: tendoaki@gmail.com (Michael Morris)

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On Thu, Jan 25, 2018 at 11:59 PM, Niklas Keller <me@kelunik.com> wrote:

> Michael Morris <tendoaki@gmail.com> schrieb am Fr., 26. Jan. 2018, 02:06:
>
>> On Thu, Jan 25, 2018 at 3:04 PM, Niklas Keller <me@kelunik.com> wrote:
>>
>> >
>> >>
>> >> $a instanceof array<string>
>> >>
>> >
>> > That might work, but array<string> should only return true if it's an
>> > array, not for anything that implements ArrayAccess.
>> >
>> >
>>
>> Related:
>>
>> On Thu, Jan 25, 2018 at 4:11 PM, Levi Morrison <levim@php.net> wrote:
>>
>> >
>> >
>> > I see no value to this operator being applied to non-array
>> > traversables.
>>
>>
>> If an array access object can't masquerade as an array it loses some of
>> its
>> value, but Niklas is right - it is important to distinguish such objects
>> from native arrays.  One solution would be to promote "iterable" to
>> keyword
>> status.  The flexibility to take any iterable will be needed I think.
>>
>> $a instanceof iterable<string>
>>
>> Would return true for anything iterable (which we can already test with
>> is_iterable() ) where all values where strings.
>>
>> On Thu, Jan 25, 2018 at 4:11 PM, Levi Morrison <levim@php.net> wrote:
>> >
>> > Our iterators cannot always be reliably rewound, such as
>> > when using generators. Checking that the generator returns only
>> > strings would consume all the input and would therefore be useless.
>>
>>
>> True - I hadn't thought of those. But as of PHP 7 generators can type
>> declare their return value.
>
>
> They can only define generator as return type, which is what they return
> when you call a generator function.
>
> Even if you could declare the return type of the generator, you'd still
> have the same problem with the yielded values.
>

See my comment about coding around morons being a pointless exercise.  You
throw an error and force the moron to fix their code.


>
> So, given `$a instanceof iterable<string>`, if
>> $a is a reference to a generator, then the engine could check the return
>> type declaration and only give true on a match without attempting to use
>> the generator.
>>
>> We can follow this pattern farther - The return of an
>> ArrayAccess::offsetGet and Iterator::current() can be similarly tested by
>> instanceof rather than actually pulling data from these methods.
>>
>> We are having the return rely on the promise of the code, but in each case
>> TypeError would be raised anyway if it breaks it's promise to instanceof
>> so
>> errors aren't being avoided.
>>
>>
>>
>> > Returns true if $a is an array (or implements array access) and that all
>> >> it's members are strings.
>> >>
>> >> $b instanceof SomeClass<string>
>> >>
>> >> Returns true if SomeClass can be iterated and contains only strings.
>> >>
>> >
>> > This would block generics with that syntax then.
>> >
>>
>> I don't understand this comment.
>>
>
> You restrict these type parameters to iterators, but generics are useful
> in a lot more places.
>

iterABLE --- not iterOR.  Two different things.

Iterable is a psuedotype in PHP covering anything that can be traversed
with foreach, including std_class, which is what I think what you mean by
generator.  There's even an existing function, is_iterable() to detect
them. `$a instanceof iterable` will return the same as `is_iterable($a);`

Generics specifically are already detectable by `$a instanceof stdClass`
`$a instanceof Iterator` detected that interface, but not arrays and
generics.
`$a instanceof iterable` would detect all three.

The similarity of the names is regrettable, but it's already in place and
can't be changed at this point.

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