Le 07/09/2011 17:35, Mark S. Miller a écrit :
On Wed, Sep 7, 2011 at 6:40 AM, David Bruant <[email protected]
<mailto:[email protected]>> wrote:
How about we adapt ideas from the "<|" proposal?
This proposal is only about initializing the prototype. I don't
see what can be adapted to work on [[Class]].
Agreed that it's quite different. My think was a bit muddy.
The [[Class]] magic that <| does derives from having a literal
expression on the right side, determining the [[Class]] of the result
while not determining the [[Prototype]] of the result. The cool thing
about depending on a literal in this position is we get to delegate to
the literal initialization logic the issue of initializing the
instance so it has the right own invariants. The proposal works
because none of the invariants associated with any existing [[Class]]
rely on the instance's [[Prototype]]. The cost if relying on syntax in
this way is we can't leverage this to create and initialize, say, a
true Date which inherits from something other than Date.prototype. We
could if we introduced a Date literal, but that's a terrible way out
of the dilemma.
The Date example also points out what's wrong about just inheriting
the [[Class]] and its associated internal vtable. Things which check
for the Date [[Class]] assume the Date invariants are maintained. A
proxy emulation of a Date must uphold these invariants.
Which suggests a bizarre idea. What if the optional third argument
were the object to serve the role of Tom's fixedProps object? Then the
proxy's [[Class]] would be the fixedProp's [[Class]], and Tom's
enforcement mechanism would magically enforce whatever invariants are
associated with [[Class]]. This should work for NodeLists and other
host objects as well.
So the third argument would be the object the proxy would become. This
sounds like a reasonable idea but is a bit different from the original
fix proposal which created a fresh object based on an object description
(pdmap).
I guess I should ask: why in the original design did the author had to
return a description of the object to be returned rather than creating
the object himself and return it? To avoid returning a proxy, maybe?
David
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