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

Brendan Eich brendan at mozilla.com
Fri Dec 16 08:59:50 PST 2011


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>
To: "Dmitry Soshnikov" <dmitry.soshnikov at gmail.com>
Cc: "Brendan Eich" <brendan at mozilla.com>, "es-discuss" <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 > 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 > 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 > 
To: "es-discuss" < 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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