Re: Enriched Descriptors, maybe ES7 ?

2014-03-10 Thread Tom Van Cutsem 
2014-03-09 21:05 GMT+01:00 Brendan Eich bren...@mozilla.com:

 Tom has experimented, IIRC. I don't know which implementations preserve
 extended property descriptor properties.


As Allen mentioned earlier, proxies should receive in their defineProperty
trap the full descriptor object as it was passed in by the user, including
any custom attributes. The proxy is free to store it, and return it from
any subsequent getOwnPropertyDescriptor trap (which is also specced so that
it can return a non-normalized descriptor object with custom attributes).

Normal (non-proxy) objects of course cannot store non-normalized
descriptors, so any custom attributes are lost. Changing this would
presumably have a big impact on implementations (which probably don't hang
on to descriptor objects at all).

If you want to experiment with custom attributes, my harmony-reflect shim
supports this for proxies:

var props = {};
var o = new Proxy({},{
  defineProperty: function(target, name, desc) {
props[name] = desc;
return true;
  },
  getOwnPropertyDescriptor: function(target, name) {
return props[name];
  }
});
Object.defineProperty(o,p,{value:42, configurable:true, hello:true})
JSON.stringify(Object.getOwnPropertyDescriptor(o,p))
// prints
// {configurable:true,
//  value:42,
//  writable:false,
//  enumerable:false,
//  hello:true } // - custom attribute preserved

Using Firefox's built-in direct proxies implementation I get a TypeError.
I'll investigate further and file a bug.

Regards,
Tom
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Re: Enriched Descriptors, maybe ES7 ?

2014-03-10 Thread David Bruant 

Le 10/03/2014 08:02, Tom Van Cutsem a écrit :
Using Firefox's built-in direct proxies implementation I get a 
TypeError. I'll investigate further and file a bug.

You already did https://bugzilla.mozilla.org/show_bug.cgi?id=601379 ;-)

David
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Re: Enriched Descriptors, maybe ES7 ?

2014-03-10 Thread Andrea Giammarchi 
Thanks Tom, I see what you mean but using proxies is a performance killer,
while I am trying to propose something that theoretically could also give a
performance boost.

I am not proposing custom descriptor attributes here, I am proposing
`type`, `arguments` (or `parameters`) and `returns` as specified/extra
descriptor properties capable to bring typed properties to, maybe, ES7

My repository already does this and it works even copying objects, if this
is done through `getOwnPropertyDescriptor`

So, custom descriptor properties a part, would ES7 consider to implement
types not only for `StructType` but also for runtime defined shapes so that
`Object.defineProperty({}, 'num', {value: 123, writable: true, type:
int32})` works same as my polyfill does already?

Thanks




On Mon, Mar 10, 2014 at 12:02 AM, Tom Van Cutsem tomvc...@gmail.com wrote:

 2014-03-09 21:05 GMT+01:00 Brendan Eich bren...@mozilla.com:

 Tom has experimented, IIRC. I don't know which implementations preserve
 extended property descriptor properties.


 As Allen mentioned earlier, proxies should receive in their defineProperty
 trap the full descriptor object as it was passed in by the user, including
 any custom attributes. The proxy is free to store it, and return it from
 any subsequent getOwnPropertyDescriptor trap (which is also specced so that
 it can return a non-normalized descriptor object with custom attributes).

 Normal (non-proxy) objects of course cannot store non-normalized
 descriptors, so any custom attributes are lost. Changing this would
 presumably have a big impact on implementations (which probably don't hang
 on to descriptor objects at all).

 If you want to experiment with custom attributes, my harmony-reflect shim
 supports this for proxies:

 var props = {};
 var o = new Proxy({},{
   defineProperty: function(target, name, desc) {
 props[name] = desc;
 return true;
   },
   getOwnPropertyDescriptor: function(target, name) {
 return props[name];
   }
 });
 Object.defineProperty(o,p,{value:42, configurable:true, hello:true})
 JSON.stringify(Object.getOwnPropertyDescriptor(o,p))
 // prints
 // {configurable:true,
 //  value:42,
 //  writable:false,
 //  enumerable:false,
 //  hello:true } // - custom attribute preserved

 Using Firefox's built-in direct proxies implementation I get a TypeError.
 I'll investigate further and file a bug.

 Regards,
 Tom

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Re: Enriched Descriptors, maybe ES7 ?

2014-03-10 Thread Tom Van Cutsem 
2014-03-10 11:10 GMT+01:00 David Bruant bruan...@gmail.com:

 Using Firefox's built-in direct proxies implementation I get a TypeError.
 I'll investigate further and file a bug.
 You already did https://bugzilla.mozilla.org/show_bug.cgi?id=601379 ;-)


Thanks for refreshing my memory on that one ;-)

But that was actually not the bug that caused my earlier code snippet to
fail. Instead it's this bug (already reported by Eddy Bruel):
https://bugzilla.mozilla.org/show_bug.cgi?id=793210

Cheers,
Tom
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