operator overloading proposal

kdex kdex at kdex.de
Wed May 11 00:21:05 UTC 2016


@Isiah: Comparing your syntax proposal to `Function.defineOperator`, it appears to me that
overloading an operator multiple times (e. g. unary/binary plus operator) might become painful,
assuming that the semantics follow the same variadic approach that regular functions do.

That is, of course, unless you intend to handle all operator overloads in a single `operator +(...args) {}`
definition. But then again, something like `Function.defineOperator` seems cleaner and suggests implicit
(optional?) type checks with its second argument.

On Dienstag, 10. Mai 2016 15:25:32 CEST Isiah Meadows wrote:
> Here's my thought, if we go with syntax.
> 
> ```js
> class Point {
>     // constructor, etc.
> 
>     operator +(other) {
>         assert(other instanceof Point)
>         return new Point(
>             this.x + other.x,
>             this.y + other.y)
>     }
> 
>     operator +=(other) {
>         assert(other instanceof Point)
>         this.x += other.x
>         this.y += other.y
>     }
> }
> ```
> 
> On Tue, May 10, 2016, 11:16 Brian Barnes <ggadwa at charter.net> wrote:
> 
> > A note on this from somebody who's entire existence seems dedicated to
> > stopping as much stuff as possible from getting GC'd, the example below:
> >
> >  >const u = new Point(5, 10);
> >  >const v = new Point(1, -2);
> >  >
> >  >const w = u + v;  // desugars to u[Symbol.add](v)
> >  >console.log(w);   // { x: 6, y: 8 };
> >
> > Could += be a special case?  i.e.,
> >
> > u+=v;
> >
> > would call:
> >
> > Class Point { ... other stuff ...
> > [whatever the syntax is](pt)
> > {
> > this.x+=pt.x;
> > this.y+=pt.y;
> > }
> > }
> >
> > instead of desugaring to:
> >
> > u=u+v;          // which would cause the creation of an object and
> >                 // leave the other to be collected
> >
> > For all I know, += might be doing such anyway in some engines, but for
> > my stuff which is a lot of 3D math that could be a performance killer.
> > It would be nice to be able to just add points and such, as long as the
> > overhead is negligible.
> >
> > [>] Brian
> >
> > On 5/10/2016 10:52 AM, Isiah Meadows wrote:
> > > I would prefer syntax + internal slots, since you'll know at creation
> > > time whether the object has overloaded operators. It's much simpler for
> > > the engine to figure out, and it's more performant because you only need
> > > to check one thing instead of worrying about inheritance, own
> > > properties, etc.
> > >
> > > Also, it would be IMHO easier to read than a symbol (the computed
> > > property syntax is ugly IMO). Using a different concept than symbols
> > > would also fit better with value types whenever any of those proposals
> > > make it into the language (either the struct or special syntax).
> > >
> > >
> > > On Tue, May 10, 2016, 04:03 G. Kay Lee
> > > <balancetraveller+es-discuss at gmail.com
> > > <mailto:balancetraveller%2Bes-discuss at gmail.com>> wrote:
> > >
> > >     Yes, I think exposing operators through well-known symbols is an
> > >     interesting idea worthy of more exploration because it's precisely
> > >     the purpose of well-known symbols to expose and allow manipulation
> > >     to previously inaccessible internal language behaviors.
> > >
> > >     On Tue, May 10, 2016 at 1:59 PM, Kevin Barabash
> > >     <kevinb at khanacademy.org <mailto:kevinb at khanacademy.org>> wrote:
> > >
> > >         > And remember that decorators are essentially just a syntax to
> > >         apply functions to objects/classes at design time, so what
> > >         you're proposing is essentially some new global function, which
> > >         is going against the current trend and effort to better
> > >         modularize/namespace all these utility functions/methods.
> > >
> > >         That's a really good point.
> > >
> > >         > It has been mentioned and discussed in numerous places over the
> > >         years, you can find more info on this with some casual googling.
> > >         For example:https://news.ycombinator.com/item?id=2983420
> > >
> > >         Thanks for the link.  I played around with sweet.js a bit over
> > >         the weekend.  Using macros should work if we went with Python
> > >         style operator overloading.  Instead of defining methods like
> > >         _ADD_, _SUB_ etc. we could create some well-known symbols, maybe
> > >         Symbol.plus, Symbol.times, etc.
> > >
> > >         ```
> > >         class Point {
> > >           constructor(x, y) {
> > >             Object.assign(this, {x, y});
> > >           }
> > >
> > >           [Symbol.add](other) {
> > >             return new Point(this.x + other.x, this.y + other.y);
> > >           }
> > >         }
> > >
> > >         const u = new Point(5, 10);
> > >         const v = new Point(1, -2);
> > >
> > >         const w = u + v;  // desugars to u[Symbol.add](v)
> > >         console.log(w);   // { x: 6, y: 8 };
> > >         ```
> > >
> > >         This would require default implementations to be defined on
> > >         Object.prototype for Symbol.plus, Symbol.times, etc.
> > >
> > >
> > >         On Sun, May 8, 2016 at 10:38 PM, G. Kay Lee
> > >         <balancetraveller+es-discuss at gmail.com
> > >         <mailto:balancetraveller+es-discuss at gmail.com>> wrote:
> > >
> > >             > Why not? The standard defines well-known symbols. Maybe
> > `@operator` could be a well known decorator (assuming decorators get
> > approved).
> > >
> > >             Well... you make something into the standard with proposals,
> > >             not why-nots, so in order to make that happen you need to
> > >             draft another proposal for well-known decorators. And
> > >             remember that decorators are essentially just a syntax to
> > >             apply functions to objects/classes at design time, so what
> > >             you're proposing is essentially some new global function,
> > >             which is going against the current trend and effort to
> > >             better modularize/namespace all these utility
> > >             functions/methods. And maybe a new mechanism could be
> > >             drafted for these new well-known decorators, so that we can
> > >             hide these new functions somewhere... but by now I hope it's
> > >             becoming clear that it's introducing way too much new
> > >             surface area for the language in exchange for one small
> > feature.
> > >
> > >             > I haven't seen any proposals for macros, could you post a
> > link?
> > >
> > >             It has been mentioned and discussed in numerous places over
> > >             the years, you can find more info on this with some casual
> > >             googling. For example:
> > >             https://news.ycombinator.com/item?id=2983420
> > >
> > >
> > >
> > >             On Sun, May 8, 2016 at 2:51 PM, Kevin Barabash
> > >             <kevinb at khanacademy.org <mailto:kevinb at khanacademy.org>>
> > wrote:
> > >
> > >                 I should update the demo code to show the `@operator`
> > >                 decorator in addition to `Function.defineOperator`.
> > >
> > >                 Initially I started out with just the `@operator`
> > >                 decorator, but that meant that each class would have to
> > >                 have knowledge of each of the classes it might want to
> > >                 interact with before hand.  Having a separate
> > >                 `defineOperator` function avoids this situation.
> > >
> > >                 It means that prototype style classes must be converted
> > >                 to the new class syntax before operator overloading
> > >                 could be used.  Lastly, there may be some cases where it
> > >                 makes sense to overload operators with existing 3rd
> > >                 party code or built-in classes, e.g. adding set
> > >                 operations to Set using operator overloading.
> > >
> > >                 > It's also apparent that the `@operator decorator` part
> > >                 of the proposal is an effort trying to address this
> > >                 issue, but it really is not the responsibility of the
> > >                 standard to try to define such a thing.
> > >
> > >                 Why not?  The standard defines well-known symbols.
> > >                 Maybe `@operator` could be a well known decorator
> > >                 (assuming decorators get approved).
> > >
> > >                 Slide 15
> > >                 from http://www.slideshare.net/BrendanEich/js-resp shows
> > >                 syntax for defining operators in value types which could
> > >                 be adapted as follows for regular classes:
> > >
> > >                 ```
> > >                 class Point {
> > >                    constructor(x, y) {
> > >                        this.x = +x;
> > >                        this.y = +y;
> > >                    }
> > >                    Point + Number (a, b) {
> > >                        return new Point(a.x + b, a.y + b);
> > >                    }
> > >                    Number + Point (a, b) {
> > >                        return new Point(a + b.x, a + b.y);
> > >                    }
> > >                    Point + Point (a, b) {
> > >                        return new Point(a.x + b.x, a.y + b.y);
> > >                    }
> > >                 }
> > >                 ```
> > >
> > >                 Having to define `+` twice for `Point + Number` and
> > >                 `Number + Point` seems like busy work, but maybe it's
> > >                 better to be explicit.  What are you thoughts about this
> > >                 syntax?
> > >
> > >                 > Another thing is that, IMHO, currently there are too
> > >                 much quirks/conventions in the proposal that feel
> > >                 non-evident and non-flexible which is destined to trip
> > >                 people over from time to time. It would be great to make
> > >                 a proposal that's simple and don't include too much
> > >                 assumptions.
> > >
> > >                 Could you elaborator what quirks/conventions might trip
> > >                 people up?
> > >
> > >                 > Finally, I'm not sure about the current status of
> > >                 macros, but last I heard of it, they say it's going to
> > >                 make its way into the standard pretty soon (TM), and
> > >                 macros can do much of the things overloading could, and
> > >                 much more.
> > >
> > >                 I haven't seen any proposals for macros, could you post
> > >                 a link?
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >                 On Sat, May 7, 2016 at 9:55 PM, G. Kay Lee
> > >                 <balancetraveller+es-discuss at gmail.com
> > >                 <mailto:balancetraveller+es-discuss at gmail.com>> wrote:
> > >
> > >                     I'd say it's way too early to ask for a champion on
> > >                     this because just a quick skimming revealed a lot of
> > >                     places that didn't add up. For example, the proposal
> > >                     suggested that overloading is primarily targeted at
> > >                     making it easier to work with user-defined classes,
> > >                     but curiously a `Function.defineOperator()` method
> > >                     is proposed instead of some syntax that feels more
> > >                     tightly integrated with the class definition syntax.
> > >
> > >                     ```
> > >
> > >                     class Point {
> > >                         constructor(x, y) {
> > >                             Object.assign(this, { x, y });
> > >                         }
> > >
> > >                         toString() {
> > >                             return `(${this.x}, ${this.y})`;
> > >                         }
> > >                     }
> > >
> > >                     Function.defineOperator('+', [Point, Point], (a, b)
> > => new Point(a.x + b.x, a.y + b.y));
> > >
> > >                     ```
> > >
> > >                     The demo code made this flaw evident - it looks like
> > >                     a giant step backward to define an instance method
> > >                     like this, don't you agree?
> > >
> > >                     It's also apparent that the `@operator decorator`
> > >                     part of the proposal is an effort trying to address
> > >                     this issue, but it really is not the responsibility
> > >                     of the standard to try to define such a thing.
> > >
> > >                     What I'd suggest is that perhaps you should rethink
> > >                     your proposed syntax and redesign it to become an
> > >                     extension of the ES6 class definition syntax.
> > >
> > >                     Another thing is that, IMHO, currently there are too
> > >                     much quirks/conventions in the proposal that feel
> > >                     non-evident and non-flexible which is destined to
> > >                     trip people over from time to time. It would be
> > >                     great to make a proposal that's simple and don't
> > >                     include too much assumptions.
> > >
> > >                     Finally, I'm not sure about the current status of
> > >                     macros, but last I heard of it, they say it's going
> > >                     to make its way into the standard pretty soon (TM),
> > >                     and macros can do much of the things overloading
> > >                     could, and much more.
> > >
> > >                     On Sun, May 8, 2016 at 8:51 AM, Kevin Barabash
> > >                     <kevinb at khanacademy.org
> > >                     <mailto:kevinb at khanacademy.org>> wrote:
> > >
> > >                         I forgot to mention in my last email that I'm
> > >                         looking for a champion for this proposal.
> > >
> > >                         On Sat, May 7, 2016 at 5:24 PM, Kevin Barabash
> > >                         <kevinb at khanacademy.org
> > >                         <mailto:kevinb at khanacademy.org>> wrote:
> > >
> > >                             Hi everyone,
> > >
> > >                             I've been working on implementing operator
> > >                             overloading and would like to submit a
> > proposal.
> > >
> > >                             I think operator overloading would be a
> > >                             useful addition to the language.  In
> > >                             particular I think it would be useful for
> > >                             defining operations on common mathematical
> > >                             object types such as complex numbers,
> > >                             vectors, matrices, and sets.
> > >
> > >                             I've create a working prototype that
> > >                             consists of:
> > >
> > >                               * babel plugin that rewrites operators as
> > >                                 function calls
> > >                               * a polyfill which defines these functions
> > >                                 and which call the correct
> > >                                 argument-specific function based on the
> > >                                 arguments' prototypes
> > >                               * Function.defineOperator which can be
> > >                                 used to define which function an
> > >                                 operator should use for the specified
> > types
> > >                               * "use overloading" directive which allows
> > >                                 users to opt-in
> > >
> > >                             More details can be found
> > >                             at
> > https://github.com/kevinbarabash/operator-overloading.
> > >                             The babel plugin can be found
> > >                             at
> > https://github.com/kevinbarabash/babel-plugin-operator-overloading.
> > >                             I also have a demo project at
> > >
> > https://github.com/kevinbarabash/operator-overloading-demo.
> > >
> > >                             The design was inspired by some of the
> > >                             slides from
> > >
> > http://www.slideshare.net/BrendanEich/js-resp.
> > >
> > >                             – Kevin
> > >
> > >
> > >
> > >
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