[RFC] Combined Comparison Operator

Hi Davey,

I've written up an RFC/Patch to gauge interest and get feedback on the
addition of a combined comparison (aka: spaceship) operator.

You can see the RFC at: https://wiki.php.net/rfc/
combined-comparison-operator

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.

Code available here (against 5.6): https://github.com/dshafik/
php-src/compare/add-spaceship-operator

I'd love to get this into 5.6, not sure if we hit feature freeze yet.
Also, not sure if it needs 2/3 majority, but assumed so as pow did?

Thoughts?

If there is interest, I'll start adding tests. They should be fairly
trivial.

Interesting shortcut operator.
I feel closure function is for the task.
I would vote 0, but close to -1 since it's only useful for sorting.
Is there any other use cases?

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

Yasuo,

Sorting is definitely it's most compelling use. It cuts down on potentially quite a bit of code:

function ($left, $right) {
if ($left[1] == $right[1]) {
return 0;
}

if ($left[1] > $right[1]) {
return 1;
}

if ($left[1] < $right[1]) {
return -1;
}
}

or (as per the RFC):

function ($left, $right) {
return $left[1] <=> $right[1];
}

--

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.

If you really need the -1/0/1 return value (sorting functions don’t), then wrap the strcmp/subtraction in a trivial sign() function.

Simon Welsh
Admin of http://simon.geek.nz/

function ($left, $right) {
if ($left[1] == $right[1]) {
return 0;
}

 if ($left[1] > $right[1]) {
      return 1;
 }

 if ($left[1] < $right[1]) {
     return -1;
 }

}

or (as per the RFC):

function ($left, $right) {
return $left[1] <=> $right[1];
}

while that example is overly nice - in real world outside a usort
callback the consumer of the function in most cases still has to do the
three if cases to use the result. So in practical terms it is limited to
usort() and then it is a custom operator people reading the code most
likely have to lookup. Typically in PHP we try to have identifiers which
can be found via Google, Google doesn't handle "special" characters
well.

johannes

Hi David,

Thanks for this proposal.

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

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

• Davey

That's why I said, it would make more sense to add a new function for comparing arrays and objects.
Why adding a new comparison operator if we could achieve the same with one or two additional functions?

And I am not sure, if this is not already possible nowadays.

For arrays you could do: array_sum($array1) - array_sum($array2)

And for objects you can define a "sum" method on your objects or a trait e.g.

trait SummableTrait {
public function sum() {
$sum = 0;
foreach (get_object_vars($this) as $value) {
$sum += $value;
}
return $sum;
}
}

You only have to use this trait in your classes and then you can do: $object1->sum() - $object2->sum()

Et voilà :-)

Christian