Tech talk on proxies and traits

Brendan Eich brendan at
Sat May 1 15:33:01 PDT 2010

On May 1, 2010, at 2:49 PM, Dmitry A. Soshnikov wrote:

> Hello Mark,
> Sunday, May 2, 2010, 1:02:36 AM, you wrote:
>> On Sat, May 1, 2010 at 1:27 PM, Brendan Eich <brendan at>  
>> wrote:
>>> On May 1, 2010, at 12:34 PM, Faisal Vali wrote:
>>>> As I read the proposal, I do wish an invoke-like trap had been
>>>> accepted - but I understand that there were some technicalities  
>>>> that
>>>> proved unresolvable.
>>> Everyone wants __noSuchMethod__
>> I don't. I want proxies instead. ;)

I meant "Everyone" to mean "many people" -- for the convenience.

> By the way, why exactly proxies? And not special meta hooks such as
> __noSuchMethod__, __construct__, __call__, __get__, __set__ and other?

Mark and Tom's write-up is on the wiki, have you read it?

Stratifying means native objects need no magic meta methods which can  
be hijacked by user code. This is important for the spec's soundness,  
as well as for security and ease of implementation/optimization.

Nothing reserved __names__, that is just a Python convention, and C,  
or really the C pre-processor I suppose. The ship has sailed. Even if  
we could reserve __names__, mixing traps and base methods is a recipe  
for spec unsoundness, insecurity, and implementation bugs and slowness.

Proxies avoid all these problems. They are truly winning, we have an  
implementation nearly done for SpiderMonkey so I can write this as an  

The only issue that nags at us is the loss of a convenient invoke trap  
that preserves evaluation order. One could be added, but it is  
tantamount to creating (or hitting a cached) Proxy, in order to  
preserve order of evaluation.


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