noSuchMethod: "funargs" + "invoke-only-phantoms"

Dmitry Soshnikov dmitry.soshnikov at gmail.com
Sat Dec 17 02:56:44 PST 2011


On 17.12.2011 9:56, Andrea Giammarchi wrote:
> if both V8 and SpiderMonkey will follow that logic to trap invoke-only 
> method, I'll do my best to promote and explain how it works and why 
> addressing anyhow does not make sense since there is nothing to 
> address being inexistent.
>

It was my main thoughts and arguments through that "never-ending initial 
thread". And this position of course makes perfect sense.

However, it may also be broken until we don't have the answer to the 
following question:

Why does a programmer have an error in the following transformation of a 
code?

Was:

lib.toRussianName("Andrea"); // ??????

Became:

var toRussianName = lib.toRussianName;
toRussianName.apply(null, ["Andrea", "Alex"]); // error, "toRussianName" 
is undefined

If you can explain it to the programmer that she should first go to the 
documentation and to see that methods such as `to<Country>Name' are 
virtual, but not real and then to use all such cases with caution, then 
this is OK. This is actually the only way to solve this issue -- to tell 
the programmer "go to the documentation and check which virtual, i.e. 
invoke-only methods you have".

In other case, you can't explain to her why she, being in JS, can't 
transform this line of a code into the second one. Can she do this? Does 
she have rights/license for this? Of course she can, of course she does.

But in all other broken cases -- I already said, I agree that this 
implementation also breaks some logic. And in the same manner you'll 
have to explain to the programmer why if she:

delete lib.toRussianName;

then it still:

typeof lib.toRussianName; // "function", Trollface ;D

So, the only answer on this topic is should be the answer on "what is 
less painful and less critical" in this case? To explain one broken 
invariants or others? Once we have answered this question, we may easily 
implement any from this design decisions.

Dmitry.

> That case would be covered eventually by no such property but this one 
> specially is trivial with Proxies, the method isn't.
>
> Te shouting is me being lazy with bold and stars trying to underlying 
> common misconception I have read around about what "problem" 
> noSuchMethod should bring, in my opinion non of them as long as the 
> behavior is well defined and clear which is, to me, the case since ever.
>
> Good to know that at least SpiderMonkey is not planning to drop it
>
> Best Regards
>
> On Fri, Dec 16, 2011 at 5:59 PM, Brendan Eich <brendan at mozilla.com 
> <mailto:brendan at mozilla.com>> wrote:
>
>     I don't think SHOUTING helps your argument.
>
>     The key point is whether and how any user of an abstraction can
>     know that a given method is first- or second-class. Some
>     frameworks such as TIBET use second-class methods only.
>
>     Others (E4X, ECMA-357 comes to mind -- users did and do trip over
>     its invoke-only methods) could segregate and document methods as
>     to which can be extracted and called later with an appropriate
>     |this|, and which are invoke-only.
>
>     But arguing your conclusion that __noSuchMethod__ is only about
>     the latter case of NOT HAVING A FUNCTION doesn't help. It's a
>     circular argument.
>
>     Abstractions of the O-O varieties have different philosophies
>     about methods, but when applied to JS, the cross-browser libraries
>     do not say "you have to know if this method is real or virtual."
>     People have not built much on __noSuchMethod__ since it's only in
>     SpiderMonkey. We lack experience in-the-large with it.
>
>     On this basis, I'm still happy to see method-missing traps
>     implementable on top of direct proxies. Users will soon be able to
>     experiment with such libraries in SpiderMonkey and V8. Then we can
>     see what we've learned. If you are right, it'll be trivial to
>     standardize one of these libraries, or even make a private-named
>     unstratified noSuchMethod trap.
>
>     /be
>
>     ----- Original Message -----
>     From: "Andrea Giammarchi" <andrea.giammarchi at gmail.com
>     <mailto:andrea.giammarchi at gmail.com>>
>     To: "Dmitry Soshnikov" <dmitry.soshnikov at gmail.com
>     <mailto:dmitry.soshnikov at gmail.com>>
>     Cc: "Brendan Eich" <brendan at mozilla.com
>     <mailto:brendan at mozilla.com>>, "es-discuss"
>     <es-discuss at mozilla.org <mailto:es-discuss at mozilla.org>>
>     Sent: Friday, December 16, 2011 8:30:47 AM
>     Subject: Re: noSuchMethod: "funargs" + "invoke-only-phantoms"
>
>     you don't use apply randomly, you use apply for methods or getters
>     knowing there is a function there.
>
>
>     __noSuchMethod__ is about NOT HAVING A FUNCTION there and if the
>     property is not defined apply should fail as well as
>     obj.undefined.apply would
>
>
>     I still do not understand why we keep mixing up getters with
>     __noSuchMethod__ behavior which is:
>     1. a "method" and not a property invocation ( no
>     obj.inexistent.apply BUT ONLY obj.inexistent() OR obj[inexistent]() )
>     2. unaddressable since a property that has not been define will
>     always be addressed as undefined ( or the __proto__ chain value )
>     3. nothing to defer, lazy call, pass through, etc etc ... once
>     again, noSuchMethod SHOULD cover 1 case, and 1 case only
>
>
>     obj.iDoNotExistHowCanAnyoneReferAtMeThen();
>
>
>     Rules behind the scene, described already in my post:
>
>
>     Syntax: object.methodName(); // inline invokaction, NO EXCEPTIONS
>     TO THIS SINGLE CASE
>     Procedure:
>     1. check if object has a property called "methodName"
>     1.1 yes, go on and throw an error if it is not callable
>     1.2 no, check if the property has a getter
>     1.2.1 yes, go on and throw an error if it is not callable
>     1.2.2 no, check if the object has a "__noSuchMethod__" fallback
>     1.2.2.1 yes, invoke that callback via cb.call(object,
>     "__noSuchMethod__", arguments)
>     1.2.2.2 no, throw an error "undefined is not a method"
>
>
>     Is above logic really that hard to implement/understand? I don't
>     think so but it looks like it's me only.
>
>
>     The described behavior as it is is never ambiguous so what is the
>     problem exactly?
>
>
>     Practical example
>
>
>
>     var o = Object.defineProperty({}, "test", {
>     get: function () {
>     return this.alias;
>     }
>     });
>     o.alias = function () {
>     alert(this.message);
>     };
>     o.message = "hello";
>
>
>     o.toString(); // __proto__ chain
>     o.alias(); // property as method
>     o.test(); // getter
>     o.noTest(); // __noSuchMethod__
>     o.test.call(o); // getter
>     o.noTest.call(o);// undefined is not a function
>
>
>     Best Regards
>
>
>     On Fri, Dec 16, 2011 at 9:54 AM, Dmitry Soshnikov <
>     dmitry.soshnikov at gmail.com <mailto:dmitry.soshnikov at gmail.com> >
>     wrote:
>
>
>     Yep, no doubt, first-class "missed" methods win -- again, because
>     the programmer can and has the complete right (by just looking at
>     one line of a code) to rewrite simple invoke to `apply' (she don't
>     have to think whether it's a virtual method or not).
>
>     The only thing I wanted is to reduce broken consequences. Well, or
>     at least to be aware about them ;)
>
>     Dmitry.
>
>
>
>
>     On Thu, Dec 15, 2011 at 9:32 PM, Brendan Eich <
>     brendan at mozilla.com <mailto:brendan at mozilla.com> > wrote:
>
>
>     Agreed there are use-cases for second-class methods, according to
>     style and taste.
>
>     The impetus for __noSuchMethod__ when I implemented it in 2003 was
>     to support the Smalltalk-based TIBET framework of Bill Edney and
>     Scott Shattuck. They religiously use a Smalltalk style of JS so do
>     not feel any second-class pain.
>
>     Other styles of JS would definitely feel pain. One size does not
>     fit all.
>
>     This is why rejecting an invoke trap is not a matter of black and
>     white, IMHO -- it's simply a desire to reduce complexity and see
>     how the result can be used by a library (a standard one, even) to
>     implement something like __noSuchMethod__.
>
>     /be
>
>
>     ----- Original Message -----
>     From: "Dmitry Soshnikov" < dmitry.soshnikov at gmail.com
>     <mailto:dmitry.soshnikov at gmail.com> >
>     To: "es-discuss" < es-discuss at mozilla.org
>     <mailto:es-discuss at mozilla.org> >
>     Sent: Thursday, December 15, 2011 5:48:37 AM
>     Subject: noSuchMethod: "funargs" + "invoke-only-phantoms"
>
>
>     Hi,
>
>     Here is the analysis of current "noSuchMethod" situation
>     implemented via proxies.
>
>     I summarized that never-ending thread from 2010 (
>     https://mail.mozilla.org/pipermail/es-discuss/2010-October/011929.html
>     ), since guys in JS community started to ask why proxies don't
>     support noSuchMethod.
>
>
>     It's written as a small article in a view of JS-code:
>     https://gist.github.com/1481018
>
>     Is there something to add? To change probably in the current Tom's
>     proposal? Etc.
>
>     P.S.: while I was writing the article, I started more to agree on
>     importance of the "extracted funargs" in this case, however the
>     "invoke-only-phantom" methods still and also (as it turns out) are
>     needed to users and required by them.
>
>     Cheers,
>     Dmitry.
>
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