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In-Reply-To: <CAHFNTweymOruLojRwcfhsAZTDrPwvQA86cK3cBziPd5diba3TQ@mail.gmail.com>
Date: Fri, 22 Jun 2018 17:03:07 -0400
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To: internals@lists.php.net
Content-Type: multipart/alternative; boundary="0000000000008065bf056f415ca3"
Subject: Re: [PHP-DEV] Equality and relative ordering of objects
From: rtheunissen@php.net (Rudi Theunissen)

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On further investigation, I'm not sure if we need both `__equals` and
`__compareTo`,
even with all the talk about contexts and the fact that an object can be
tested for
equality and not necessarily ordering as well. If we take out the
`__equals` method
and only include `__compareTo`, we can allow the user to return NULL to
indicate
that the object doesn't support the comparison that is being done. So the
return
values of `__compareTo` then becomes:

```
 1:    Greater than
-1:    Less than
 0:    Equal to, ==
 NULL: Unsupported, fall back to default behaviour.
```
In the case of an object returning NULL, we can fall back to the default
behaviour,
which is equivalent to the `compare` handler returning FAILURE, which then
falls
through to the `compare_objects` handler.

I think this will be less confusing and much easier to implement.

It's interesting to note that Java's `Comparable` interface considers a
0-return
to indicate equality, where a `==` would compare references in the same way
PHP's `===` would. So in dropping the `__equals` method, we're slightly more
aligned with Java, even though that's not exactly the goal here. :p

On Fri, 22 Jun 2018 at 13:55, Rudi Theunissen <rtheunissen@php.net> wrote:

> What's the best place to override == internally? `do_operation` or a new
> object handler?
> I'd like to separate equality from compare_function.. or should we ignore
> `__equals `
> and assume that the values are equal if `__compareTo` returns 0?
>
> Here's some context: I'm modifying `is_equal_function` to check for an
> `__equals`
> implementation if the value is an object, which I think should work, but
> it's not clear how
> an internal object (like the ds structures, for example) should override
> ==.
>
> `do_operation` seems like a good choice for this, but I wanted to check
> with you all first.
>
>
>
> On Fri, 22 Jun 2018 at 13:06, Rudi Theunissen <rtheunissen@php.net> wrote:
>
>> > Yes, that's the type of thing that I think needs to be included as
>> > part of the RFC.
>> >
>> > Including a list of all the (or at least the important) functions that
>> > would be affected by this RFC should be made both for clarity and so
>> > that people can think through any edge cases.
>>
>>
>> Absolutely. I was hoping to gather some thoughts and opinions first while
>> I
>> work on the implementation before I submit an official RFC. I'll make
>> sure to
>> include what you've mentioned, I completely agree.
>>
>> On Fri, 22 Jun 2018 at 11:14, Dan Ackroyd <danack@basereality.com> wrote:
>>
>>> On 22 June 2018 at 12:31, Rudi Theunissen <rtheunissen@php.net> wrote:
>>>
>>> >
>>> >> I think if you want to push the RFC forward, a really quite strong
>>> >> case needs to be made for why having it be a language level feature is
>>> >> so much better (or even at all better) than having it be implemented
>>> >> in userland.
>>>
>>> >
>>> >
>>> > 1. You can't override the behaviour of `<`, `<=`, `>`, `>=`, `==`,
>>> `!=` with
>>> > a userland implementation.
>>> > 2. Therefore, you won't be able to affect the internals of array
>>> functions
>>> > like `in_array`, `sort` etc.
>>>
>>>
>>> Yes, that's the type of thing that I think needs to be included as
>>> part of the RFC.
>>>
>>> Including a list of all the (or at least the important) functions that
>>> would be affected by this RFC should be made both for clarity and so
>>> that people can think through any edge cases.
>>>
>>> cheers
>>> Dan
>>>
>>

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