Re: [RFC] Combined Comparison Operator

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