New paper: "Distributed Electronic Rights in JavaScript"

David Bruant bruant.d at gmail.com
Tue Jan 15 12:49:53 PST 2013


Le 15/01/2013 19:19, Kevin Reid a écrit :
> On Tue, Jan 15, 2013 at 2:20 AM, David Bruant <bruant.d at gmail.com 
> <mailto:bruant.d at gmail.com>> wrote:
>
>     Practice of the event loop model in JavaScript has proven that the
>     share-nothing model has limitations. In my opinion, one of the
>     reasons WebWorkers aren't used is that the share-nothing model
>     imposes to copy data when one wants 2 WebWorkers to communicate.
>     This resulted in the addition of Transferable objects in
>     JavaScript [1]. Rust introduced the notion of unique pointer [2]
>     for equivalent reasons.
>
>
> From a capability viewpoint, there are non-performance reasons to have 
> the same pattern, even within a given event loop, namely resources 
> which may be transferred with observably exclusive access (ownership); 
> the pattern is to have an operation on the resource which generates a 
> new reference to it (i.e. a new object, from the OO perspective) and 
> makes the old one useless ("revoked").
Interesting. It reminds me that JavaScript does not have a notion of 
internal and external code with regard to an object. Anyone with access 
to the object can equivalently modify it (add, delete properties for 
instance).
On object can't at the same time defend its integrity and modify its own 
shape (I guess it's possible with proxies now).

I don't know why anyone would want to do that, but if you want to model 
a caterpillar becoming a butterfly, it's a bit complicated in JavaScript 
without proxies. The caterpillar has a "crawl" method and if we want the 
same object (same identity) to eventually become a butterfly with a 
"fly" method (but no crawl method), the object has to remain extensible 
and the crawl property has to be configurable. The problem is that any 
outsider can mess around with the properties.
The idea of generating a new object out of an old one which becomes 
useless is interesting, but people holding a reference to the 
caterpillar may expect to have a reference to a butterfly eventually. 
The problem with a new identity is that people holding a reference to 
the caterpillar now have a useless reference and may not hold the 
reference to the butterfly.

Where have you seen the "create new object from old one" pattern used? 
It sounds interesting, but I can't think of where I'd use it.

David
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