Overriding Map/etc with get/set hooks?

Allen Wirfs-Brock allen at wirfs-brock.com
Wed May 22 15:43:33 PDT 2013

On May 22, 2013, at 7:21 PM, Tab Atkins Jr. wrote:

>> -ride the same number of @@ methods so I don't see a major gain in that approach.
> [[MapData]] is just a list of tuples.  All I need for my spec (and for
> future specs that want something Map-like) is the ability to define my
> own list of tuples (linked to another object), and the ability to
> intercept sets/deletes so I can do coercion and adjustment of other
> objects.

[[MapData]] is a specification abstraction for an implementation chosen data structure.  The spec. only describes the semantics that it must be able to represent.  It is not necessarily (and hopefully isn't) implemented as a list of tuples. Regardless, it is only directly accessible at the implementation level of a ES engine.  Neither you or anybody else can directly interact with it.  However, you can indirectly interact with  [[MapData]]  through the built-in [[MapData]] methods.
> Unless I'm completely missing something, there are at most 4 "basic"
> things to override, the same 4 things that you override to make an
> "object map": create/read/update/delete.
> Is it really more complicated than this?  If so, how?

as complicated as this:

class StringMap extends Map {
   delete(key) {return super(String(key));
   get(key) {return super(String(key));
   has(key) {return super(String(key));
   set(key, value) {return super(String(key), value));


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