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Subject: Re: [RFC] Spaceship operator RFC
From: smalyshev@gmail.com (Stanislav Malyshev)

Hi!

> There is the following example in the RFC:
> 
>     // only values are compared
>     $a = (object) ["a" => "b"];
>     $b = (object) ["b" => "b"];
>     echo $a <=> $b; // 0
> 
> But the actual result is currently 1, not 0.

Ahh, I see. I think it's the mistake in the RFC. These objects are not
equal, so <=> can not return 0. These objects are compared as hashtables
(see zend_hash_compare), since $a has key "a" and $b does not,
comparison returns 1. Since objects by default are not well-ordered,
comparison does not follow the rules of order, i.e. it may happen that
both $a > $b and $b > $a. That's how compare_function works and always
worked, and <=> is just a call to that function.

> When there is no "right" value, why not raising E_NOTICE at least.  It

I'm not a big fan of throwing too many notices. They are usually not
very helpful an din this case it would be not easy to distinguish
between intentional and unintentional use.

> appears to me that returning 1 (as "undefined") without further notice
> is too misleading, as it suggests that $a is greater than $b, but that
> is not true: ($a > $b === false).

$a > $b being false is an artifact of how ">" works in the engine - $a >
$b is essentially ($b < $a). Since in this case both $a > $b and $b >
$a, the result of ($b < $a) is false. That's what you get when you
compare non-well-ordered things...

-- 
Stas Malyshev
smalyshev@gmail.com