Another idea would be to mimic Ruby's coerce protocol (http://www.engineyard.com/blog/2010/ruby-tips-numeric-classes/). Essentially, inside of the definition of op(other), if you know how to operate on a given object, you do it. Otherwise, you call other.coerce(this), which returns a tuple of objects (ret) that can be operated on. Then you can do ret[0].op(ret[1]). If the coercion can't be done, coerce can throw and the operator can continue with normal failure patterns.
-----Original Message----- From: es-discuss-boun...@mozilla.org [mailto:es-discuss-boun...@mozilla.org] On Behalf Of François REMY Sent: Monday, January 10, 2011 4:07 AM To: Erik Corry; thaddee yann tyl Cc: es-discuss@mozilla.org Subject: Re: Operator Overloading ?Well, you could implement BigNums with this proposal. You just need to make the assumption the browser use int32 to store integer numbers smaller than the max limit. Then, you build up an array that represent the big number, where arr[0] is its part from 0 to 2^32-1, arr[1] its part (=the bytes) from 2^31 to 2^64-1, and the like. You could also rely on something more subtile and less hazardous if you prefer. Regarding the a+bi problem, I may have a solution : I propose the following methods : a.canAdd(b), return true if a.add(b) can succeed. The default a.canAdd(b) method would check if "b" can be converted into the type of "a" using b.convertTo(a.constructor) or a.constructor.convertFrom(b). The default Function.prototype.canConvertFrom(b) would return true only if "b" is of type (or inherits from type) "this". In this case, the Complex class should implements some conversion logic to implement [[Number -- (widening) -> Complex]] and [[Complex -- (narrowing) -> Number]]. a = 1; b = new Complex(0,1); // b = i := sqrt(-1) a+b; ---> a.canAdd(b) ---> b.canConvertTo(Number) : no (because it has a complex part != 0) ---> Number.canConvertFrom(b) : no (because UA don't have this implemented) ---> no (a+b is not evaluted as a.addRight(b)) ---> b.canAdd(a) ---> a.canConvertTo(Complex) : no (because UA don't have this implemented) ---> Complex.canConvertFrom(a) : yes (because it's implemented by the user) ---> yes ----> a+b is evaluated as b.addLeft(a); When a.canAdd(b) && b.canAdd(a) AND a.operatorPriority==b.operatorPriority, a.addRight(b) is called. I suggest to use some special syntax for those additions, and not use a true property called "add", because it can mess up many already-written code. What about Complex.prototype = { operator add: function(b) { b=Complex.convertFrom(b); return new Complex(this.a+b.a, this.b+b.b); }, operator canConvertFrom: function(b) { return b.constructor==Complex||typeof(b)=="number"; }, .... // as no operators for addLeft/addRight are defined, addLeft and addRight are mapped to "add" (commutativity is implied). // as no operator for multiply is defined, default Object.prototype.[operator]multiply apply, which lead to an error if used with non-Number objects. } and Object.defineOperator/Object.getOperatorDescriptor/... ? BTW, as it may cause huge difficulties for UAs, I propose to have the operators of String, Number, Date (& others) marked as read-only. Regards, François -----Message d'origine----- From: Erik Corry Sent: Monday, January 10, 2011 11:12 AM To: thaddee yann tyl Cc: es-discuss@mozilla.org Subject: Re: Operator Overloading 2011/1/10 thaddee yann tyl <thaddee....@gmail.com>: > I see no reason to name the "floordiv" trap that way. Python has a Agreed. On a slightly more high level note it seems like there is a very large number of complex proposals being poured into Harmony. If they are all implemented the language will become unwieldy and complex both for users and implementers. Is there a sense in which we have a 'complexity budget' or does the committee feel we can add all proposals to the language? On the concrete proposal I note that the strawman claims this can be used to implement bignums, but it seems to me there is no way to implement storage of arbitrary size so that would appear to be impossible. Am I missing something. Another question: As I read the proposal, the dispatch is on the left hand side of binary operators. Does the proposal have a way for a+b to work where a is an old-fashioned number and b is a complex? -- Erik Corry _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
