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Date: Fri, 14 Feb 2014 11:44:20 +0100
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To: Davey Shafik <davey@php.net>
Cc: PHP Internals <internals@lists.php.net>, Pierre Joye <pierre.php@gmail.com>, 
	Simon J Welsh <simon@simon.geek.nz>, Christian Stoller <stoller@leonex.de>
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Subject: Re: [PHP-DEV] [RFC] Combined Comparison Operator
From: jpauli@php.net (Julien Pauli)

On Thu, Feb 13, 2014 at 7:04 PM, Davey Shafik <davey@php.net> wrote:
> On 2/13/14, 12:14 PM, Pierre Joye wrote:
>>
>> Hi David,
>>
>> Thanks for this proposal.
>>
>> On Feb 13, 2014 10:30 PM, "Davey Shafik" <davey@php.net> wrote:
>>>
>>>
>>> On 2/13/14, 2:19 AM, Christian Stoller wrote:
>>>>
>>>>
>>>> Davey Shafik <davey@php.net> wrote:
>>>>>
>>>>>
>>>>> This adds a new operator "(expr) <=> (expr)" that returns 0 if both
>>>>> operands are equal, 1 if the left is greater, and -1 if the right is
>>>>> greater.
>>>>>
>>>>> It works with all types (just as well as <, <=, >=, > work) and is
>>>>> great
>>>>> for usort() callbacks for example.
>>>>>
>>>>
>>>> Why not using `$a - $b` instead of `$a <=> $b`?
>>>>
>>>>
>>>> Simon J Welsh <simon@simon.geek.nz> wrote:
>>>>>
>>>>>
>>>>> The only real case I see for this is to save some boilerplate when
>>>>> dealing with arrays. Strings have strcmp(), numbers have subtraction
>>>>> And when you're sorting objects, you probably want to be doing
>>>>> the comparison on some string/numeric property.
>>>>>
>>>>
>>>> Agreed! It would make more sense to write a comparison function for
>>
>> arrays/objects.
>>>>
>>>>
>>>>
>>>> Best regards
>>>> Christian
>>>>
>>>
>>> This operator DOES work on arrays/objects. The fact it also works on
>>
>> scalar values is a bonus if that's how you want to look at it :P
>>
>> This new operator doea not look too useful to me but here is one comment
>> about objects handling:
>>
>> It compares only values, seems to be the only solution but the actual
>> usage
>> for that is rather inexistent as it compares apples and pears, or am I
>> missing something?
>>
>> Cheers,
>> Pierre
>>
>
> So, this behavior can definitely be changed -- preserving the current
> behavior of == for the 0 value, and then we can go two different ways for
> 1/-1:
>
> - Compare only like-for-like keys, ignoring extra keys
> - Compare like-for-like keys, and count the number of additional keys are
> being great. So: if they match on all common keys, but left has 3 additional
> keys, and right has 4, right is greater than left.
>
> It's definitely tough to get the semantics right. But: the behavior is also
> currently identical to $obj <= $obj2, etc. I felt that consistency was most
> important.
>
> The logical next step with this operator is to add a "Comparable"
> "interface" like ruby (not saying it has to be an interface, magic method
> also works), that allows the objects themselves to define the comparison
> behavior, so you could do:
>
> class Foo {
>     function __compare($right) {
>          // logic here
>     }
> }
>
> $left = new Foo;
> $right = new Foo;
>
> $left <=> $right; // Same as $left->__compare($right);

Please, don't.

Comparable has already been discussed many times, and has its own RFC and topic.
https://wiki.php.net/rfc/comparable
Don't mix things.
Comparable is another idea than adding a new operator.

Julien