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php

instance version of match ?

php.internals

Karoly Negyesi

4 years ago

Hi,

May I suggest adding a little "instanceof" magic to match? Like this:

match ($object) {
Someinterface => 'foo',
AnotherInterface => 'bar',
}

this can not clash with any existing code as using identifiers like this
are a syntax error currently.

Currently you could do the same with

match (true) {
$object instanceof Someinterface::class => 'foo',
$object instanceof AnotherInterface::class => 'bar',
}

Indeed, the former could be considered syntactic sugar for the latter. And
I do not think there's any ambiguity here for the casual reader or is it
just me who thinks no other sensible reading is possible?

Thanks for your consideration.

Karoly Negyesi

Weirdan

4 years ago

On Mon, Mar 28, 2022 at 7:56 PM Karoly Negyesi <karoly@negyesi.net> wrote:

> match ($object) {
>   Someinterface => 'foo',
>   AnotherInterface => 'bar',
> }
>
> this can not clash with any existing code as using identifiers like this
> are a syntax error currently.

That's valid code actually, see https://3v4l.org/BEcE4

Robert Landers

4 years ago

On Tue, Mar 29, 2022 at 3:47 AM Bruce Weirdan <weirdan@gmail.com> wrote:

>
> On Mon, Mar 28, 2022 at 7:56 PM Karoly Negyesi <karoly@negyesi.net> wrote:
> > match ($object) {
> >   Someinterface => 'foo',
> >   AnotherInterface => 'bar',
> > }
> >
> > this can not clash with any existing code as using identifiers like this
> > are a syntax error currently.
>
> That's valid code actually, see https://3v4l.org/BEcE4
>
> --
> PHP Internals - PHP Runtime Development Mailing List
> To unsubscribe, visit: https://www.php.net/unsub.php
>

It can be modified to produce ambiguous code however:

const SomeInterface = 1;
const AnotherInterface = 2;

interface SomeInterface {}
interface OtherInterface {}
$object = new class implements SomeInterface {};

var_dump(
match (true) {
$object instanceof SomeInterface => 'foo',
$object instanceof AnotherInterface => 'bar',
}
);

We can see that `SomeInterface` will resolve the interface and not the
constant.

I think what they are proposing is that when the match is an object,
and the branches are class/interface/etc names, it should just do an
`instanceof` operation instead of a value-equals operation.

Rowan Collins

4 years ago

On 29/03/2022 11:59, Robert Landers wrote:

>          $object instanceof AnotherInterface => 'bar',
>
> We can see that `SomeInterface` will resolve the interface and not the
> constant.

Yeah, the instanceof operator is magic in that regard - it has a special
parsing rule to consume the next token and avoid it being evaluated as a
constant.

> I think what they are proposing is that when the match is an object,
> and the branches are class/interface/etc names, it should just do an
> `instanceof` operation instead of a value-equals operation.

That wouldn't work, because the type of value passed to match() can vary
at run-time, but you'd need to compile the expression one way or the other.

If it did work, it would be extremely confusing:

function example(string|object $input) {
    return match($input)  {
          SomeClass => 'found class',
         SOME_CONSTANT => 'found constant',
    };
}
var_dump( example(new SomeClass) );
var_dump( example(SOME_CONSTANT) );

Do both of those matches succeed? What if I set `const SomeClass =
'hello';`?


So unfortunately we need some extra syntax to say that something should
be an instanceof check, and therefore a class name.

Regards,

--
Rowan Tommins
[IMSoP]

Thomas Nunninger

4 years ago

Hi,

Am 29.03.22 um 14:34 schrieb Rowan Tommins:

> On 29/03/2022 11:59, Robert Landers wrote:
>>          $object instanceof AnotherInterface => 'bar',
>>
>> We can see that `SomeInterface` will resolve the interface and not the
>> constant.
>
>
> Yeah, the instanceof operator is magic in that regard - it has a special
> parsing rule to consume the next token and avoid it being evaluated as a
> constant.
>
>
>> I think what they are proposing is that when the match is an object,
>> and the branches are class/interface/etc names, it should just do an
>> `instanceof` operation instead of a value-equals operation.
>
>
> That wouldn't work, because the type of value passed to match() can vary
> at run-time, but you'd need to compile the expression one way or the other.
>
> If it did work, it would be extremely confusing:
>
> function example(string|object $input) {
>      return match($input)  {
>            SomeClass => 'found class',
>           SOME_CONSTANT => 'found constant',
>      };
> }
> var_dump( example(new SomeClass) );
> var_dump( example(SOME_CONSTANT) );
>
> Do both of those matches succeed? What if I set `const SomeClass =
> 'hello';`?
>
>
> So unfortunately we need some extra syntax to say that something should
> be an instanceof check, and therefore a class name.

While I liked the intention of Karoly, I did not like the proposed magic.

Would it be an idea (and possible) to extend the syntax somehow like:

$result = match ($value) {
instanceof MyObject => ...,

>= 42 => ...,

!== 5 => ...
};

to be equivalent to:

$result = match (true) {
$value instanceof MyObject => ...,
$value >= 42 => ...,
$value !== 5 => ...
};


Regards
Thomas

Arnaud.lb

4 years ago

On mardi 29 mars 2022 15:33:41 CEST Thomas Nunninger wrote:

> Hi,
>
> Am 29.03.22 um 14:34 schrieb Rowan Tommins:
> > On 29/03/2022 11:59, Robert Landers wrote:
> >>          $object instanceof AnotherInterface => 'bar',
> >>
> >> We can see that `SomeInterface` will resolve the interface and not the
> >> constant.
> >
> > Yeah, the instanceof operator is magic in that regard - it has a special
> > parsing rule to consume the next token and avoid it being evaluated as a
> > constant.
> >
> >> I think what they are proposing is that when the match is an object,
> >> and the branches are class/interface/etc names, it should just do an
> >> `instanceof` operation instead of a value-equals operation.
> >
> > That wouldn't work, because the type of value passed to match() can vary
> > at run-time, but you'd need to compile the expression one way or the
> > other.
> >
> > If it did work, it would be extremely confusing:
> >
> > function example(string|object $input) {
> >
> >      return match($input)  {
> >            SomeClass => 'found class',
> >           SOME_CONSTANT => 'found constant',
> >      };
> >
> > }
> > var_dump( example(new SomeClass) );
> > var_dump( example(SOME_CONSTANT) );
> >
> > Do both of those matches succeed? What if I set `const SomeClass =
> > 'hello';`?
> >
> >
> > So unfortunately we need some extra syntax to say that something should
> > be an instanceof check, and therefore a class name.
>
> While I liked the intention of Karoly, I did not like the proposed magic.
>
> Would it be an idea (and possible) to extend the syntax somehow like:
>
> $result = match ($value) {
>      instanceof MyObject => ...,
>
>      >= 42 => ...,
>
>      !== 5 => ...
> };
>
> to be equivalent to:
>
> $result = match (true) {
>      $value instanceof MyObject => ...,
>      $value >= 42 => ...,
>      $value !== 5 => ...
> };
>
>
> Regards
> Thomas

I like this.

The pattern matching RFC may also cover this:
https://wiki.php.net/rfc/pattern-matching

-- Arnaud

azjezz

4 years ago

On Tuesday, March 29th, 2022 at 12:55 AM, Karoly Negyesi <karoly@negyesi.net> wrote:

> Hi,
>

> May I suggest adding a little "instanceof" magic to match? Like this:
>

> match ($object) {
>

> Someinterface => 'foo',
>

> AnotherInterface => 'bar',
>

> }
>

> this can not clash with any existing code as using identifiers like this
>

> are a syntax error currently.
>

> Currently you could do the same with
>

> match (true) {
>

> $object instanceof Someinterface::class => 'foo',
>

> $object instanceof AnotherInterface::class => 'bar',
>

> }
>

> Indeed, the former could be considered syntactic sugar for the latter. And
>

> I do not think there's any ambiguity here for the casual reader or is it
>

> just me who thinks no other sensible reading is possible?
>

> Thanks for your consideration.
>

> Karoly Negyesi

Hi Karoly,

As mentioned by Bruce, this syntax is already valid, therefor, it can't be used.

what you are looking for is pattern-matching, see "`match()` enhancement" section in the RFC: https://wiki.php.net/rfc/pattern-matching

Regards,

Saif Eddin Gmati.