On Tue, Sep 17, 2024 at 2:56 AM Lynn <kja...@gmail.com> wrote: > > > On Sat, Sep 14, 2024 at 11:51 PM Jordan LeDoux <jordan.led...@gmail.com> > wrote: > >> Hello internals, >> >> This discussion will use my previous RFC as the starting point for >> conversation: https://wiki.php.net/rfc/user_defined_operator_overloads >> >> There has been discussion on list recently about revisiting the topic of >> operator overloads after the previous effort which I proposed was declined. >> There are a variety of reasons, I think, this is being discussed, both on >> list and off list. >> >> 1. As time has gone on, more people have come forward with use cases. >> Often they are use cases that have been mentioned before, but it has become >> more clear that these use cases are more common than was suggested >> previously. >> >> 2. Several voters, contributors, and participants have had more time >> (years now) to investigate and research some of the related issues, which >> naturally leads to changes in opinion or perspective. >> >> 3. PHP has considered and been receptive toward several RFCs since my >> original proposal which update the style of PHP in ways which are congruent >> with the KIND of language that has operator overloads. >> >> I mentioned recently that I would not participate in another operator >> overload RFC unless I felt that the views of internals had become more >> receptive to the topic, and after some discussion with several people >> off-list, I feel that it is at least worth discussing for the next version. >> >> Operator overloads has come up as a missing feature in several >> discussions on list since the previous proposal was declined. This includes: >> >> [RFC] [Discussion] Support object type in BCMath [1] >> >> Native decimal scalar support and object types in BcMath [2] >> >> Custom object equality [3] >> >> pipes, scalar objects and on? [4] >> >> [RFC][Discussion] Object can be declared falsifiable [5] >> >> The request to support comparison operators (>, >=, ==, !=, <=, <, <=>) >> has come up more frequently, but particularly in discussion around linear >> algebra, arbitrary precision mathematics, and dimensional numbers (such as >> currency or time), the rest of the operators have also come up. >> >> Typically, these use cases are themselves very niche, but the >> capabilities operator overloads enable would be much more widely used. From >> discussion on list, it seems likely that very few libraries would need to >> implement operator overloads, but the libraries that do would be well used >> and thus MANY devs would be consumers of operator overloads. >> >> I want to discuss what changes to the previous proposal people would be >> seeking, and why. The most contentious design choice of the previous >> proposal was undoubtedly the `operator` keyword and the decision to make >> operator overload implementations distinct from normal magic methods. For >> some of the voters who voted yes on the previous RFC, this was a "killer >> feature" of the proposal, while for some of the voters who voted no it was >> the primary reason they were against the feature. >> >> There are also several technical and tangentially related items that are >> being worked on that would be necessary for operator overloads (and were >> originally included in my implementation of the previous RFC). This >> includes: >> >> 1. Adding a new opcode for LARGER and LARGER_OR_EQUAL so that operand >> position can be preserved during ALL comparisons. >> >> 2. Updating ZEND_UNCOMPARABLE such that it has a value other than -1, 0, >> or 1 which are typically reserved during an ordering comparison. >> >> 3. Allowing values to be equatable without also being orderable (such as >> with matrices, or complex numbers). >> >> These changes could and should be provided independent of operator >> overloads. Gina has been working on a separate RFC which would cover all >> three of these issues. You can view the work-in-progress on that RFC here: >> https://github.com/Girgias/php-rfcs/blob/master/comparison-equality-semantics.md >> >> I hope to start off this discussion productively and work towards >> improving the previous proposal into something that voters are willing to >> pass. To do that, I think these are the things that need to be discussed in >> this thread: >> >> 1. Should the next version of this RFC use the `operator` keyword, or >> should that approach be abandoned for something more familiar? Why do you >> feel that way? >> >> 2. Should the capability to overload comparison operators be provided in >> the same RFC, or would it be better to separate that into its own RFC? Why >> do you feel that way? >> >> 3. Do you feel there were any glaring design weaknesses in the previous >> RFC that should be addressed before it is re-proposed? >> >> 4. Do you feel that there is ANY design, version, or implementation of >> operator overloads possible that you would support and be in favor of, >> regardless of whether it matches the approach taken previously? If so, can >> you describe any of the core ideas you feel are most important? >> >> Jordan >> >> External Links: >> >> [1]: https://externals.io/message/122735 >> >> [2]: https://externals.io/message/122994 >> >> [3]: https://externals.io/message/121387 >> >> [4]: https://externals.io/message/120822 >> >> [5]: https://externals.io/message/118971 >> >> > I'm not experienced with other languages and overloading, so consider this > reply as me not knowing enough about the subject. Rowan asked an > interesting question: "Are we over-riding *operators* or *operations*?" > which made me think about behaviors as a 3rd alternative. Instead of > individual operator overloading, could classes define how they would act as > certain primitives or types that have overloading under the hood? We have > `Stringable` with `__toString`, which might not be the best example but > does point in a similar direction. I don't know if this is a direction > worth exploring but wanted to at least bring it up. > > ```php > interface IntBehavior { > public function asInt(): int; > } > > class PositiveInt implements IntBehavior { > public readonly int $value; > public function __construct(int $value) { > $this->value = max(0, $value); > } > public function asInt(): int { > return $this->value; > } > } > > var_dump(10 + new PositiveInt(5)); // 15 > var_dump(new PositiveInt(10) + 15); // 25 > var_dump(new PositiveInt(100) + new PositiveInt(100)); // 200 > > // leaves it to the developer to do: > $number = new PositiveInt(new PositiveInt(10) + 5); > ``` > > I actually did explore something like this during my initial design phases before ever bringing it up on list the first time. I decided that it was certainly useful, and perhaps even something I would also want, but did not solve the problem I was trying to solve.
The problem I was trying to solve involved lots of things that cannot be represented well by primitive types (which is presumably why they are classes in the first place). Things like Complex Numbers, Matrices, or Money. Money can be converted to a float of course (or an int depending on implementation), but Money does not want to be added with something like request count, which might also be an int. Or if it does, it probably wants to know exactly what the context is. There are lots of these kinds of value classes that might be representable with scalars, but would lose a lot of their context and safety if that is done. On the other hand, Money would probably not want to be multiplied with other Money values. What would Money squared mean exactly? Things like this are very difficult to control for if all you provide is a way to control casting to scaar types. Jordan
