Suggestions

Nicolas Cannasse ncannasse at motion-twin.com
Wed Jun 28 23:06:26 PDT 2006


 >> - how you will support interitance ? Will you be able to create your
 >> own prototype-chains ? In haxe you can "implements" classes. Be able
 >> to add add object in the subtyping relation would help.
 >
 > Not sure I follow you here.  You can already create arbitrary prototype
 > chains in ECMAScript:
 >
 >   function makeInheritedHash (parent) {
 >     if (parent) {
 >       function xtor() {};
 >       xtor.prototype = parent;
 >       return new xtor();
 >     }
 >     return new Object;
 >   };

Yes but it's a single list.
When you start having interfaces in the language, it means that you have 
several supertypes. It would be interesting to access/modify this 
supertype list used for runtime subtyping.

 >> - the ability to create "naked" objects, with no prototype, and no
 >> magic field, so every field of the object can be freely manipulated.
 >> It would be nice to be able to idenpendantly set the object prototype
 >> and set the "field" prototype. For instance Neko gives prototype
 >> access through primitives $objgetproto and $objsetproto instead of
 >> giving "magic" access through .prototype or __proto__.
 >
 > This can be simulated in current ECMAScript by filtering with
 > hasOwnProperty, but I agree that it is a wart that is too easy to
 > stumble over (using an Object as a HashTable and not realizing that
 > there are some keys 'already defined'). I think this could be solved by
 > letting you set a constructor's prototype to null, but the spec would
 > have to specifically state that this must be supported

Yes for example this works on current Safari JS implementation I think.

 > (it would have to
 > define what operations must work on objects with no prototype).  Making
 > an object with a null prototype breaks several current implementations.

Accessing fields for reading/writing looks enough.

 >> - exceptions with complete stack traces : not as strings but as
 >> objects, so we can easily extract the line numbers and replace them by
 >> the original language file/line numbers. That can also be implemented
 >> by the ability to add specific comments in generated code, such as :
 >
 > Isn't this really just part of your introspection request?  IWBN to have
 > introspection interfaces to the execution context.  As long as we are
 > re-implementing Lisp, eval needs to take an execution context as an
 > argument:
 > 
http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-26.html#%25_idx_4230.
 > (This would also be helpful writing a debugger).

Actually, there is another way to do this. If the exception stack trace 
gives the file+line table representation the stack, then we can do 
appropriate replacements by remaping line X of the generated JS to the 
file/line of the original files.

 >> - "magic" fields __resolve, __call and __get/__set (array accesses)
 >> would help to implement several kind of highlevel features 
transparently.
 >
 > Please elaborate?

For instance, when an unknown field is accessed in ActionScript2, 
__resolve is called instead (if exists). It has an argument which is the 
field name.

When an object is used as a function and called, the __call method could 
be invoked with the list of arguments.

Here's an exemple of what is happening at runtime :

o.unknownField    => o.__resolve("unknownField")
o.xxx = 0         => o.__setfield("xxx",0)
o(1,2,3)	  => o.__call(1,2,3)
o[56]		  => o.__get(56) // or __resolve(56) ?
o[56] = 5	  => o.__set(56,5) // or __setfield(56,5) ?

This can be optimized correctly by storing some bits in the object 
telling which magic accessor it has. This then only require one 
additional test in some specific cases.

Nicolas



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