On 10/13/2011 09:23 AM, John J Barton wrote:
On Thu, Oct 13, 2011 at 8:32 AM, Allen Wirfs-Brock
<al...@wirfs-brock.com <mailto:al...@wirfs-brock.com>> wrote:
..
My understanding of <| is that it sets the [[prototype]] property
and nothing else. Consequently, I think that the semantics of
"Array <| function(...){}" is to create a function with the
prototype chain as follow:
(anon function) --> Array --> Function.prototype -->
Object.prototype --> null
And unless otherwise specified, (anon function).prototype is a
fresh object inheriting from Object.prototype (not Array.prototype)
that was the original idea but a couple of months ago the <| spec
was updated:
"If the LHS operand has a property named |prototype| and the RHS
operand is a function expression then the [[Prototype]] of the
function object is set to the LHS object and the |prototype|
property of the new function is set to a new object whose
[[Prototype]] is the value of the LHS’s |prototype| property."
(http://wiki.ecmascript.org/doku.php?id=harmony:proto_operator )
For me this paragraph is a puzzle. A lot of the problem for me is "a
property named prototype" vs [[Prototype]], two things with the same
owner and same name to first order, but completely different in
meaning. In addition we have function 'expression', function
'object', 'new' function and 'new' object.
I find the [[prototype]] prototype language confusing. Sometimes it
helps me to understand the spec by (temporarily) replacing all
occurrences of [[prototype]] with [[inherits from]]. Then that
paragraph reads:
"If the LHS operand has a property named |prototype| and the RHS operand
is a function expression then the [[inherits from]] of the function
object is set to the LHS object and the |prototype| property of the new
function is set to a new object whose [[inherits from]] is the value of
the LHS’s |prototype| property."
In pseudo code...
if (LHS.hasOwnProperty("prototype")) {
LHS.prototype <-- inherits from -- RHS.prototype (a new object
created by <| )
LHS <-- inherits from -- RHS (a new function created by <| and the
expression to the right of <| )
}
Or in more detail and browser specific pseudo code...
LHS = make_object_from_source_code_string(..left of <|..);
if (is_source_code_string_a_function_expression(..right of <|..)) {
if (LHS.hasOwnProperty("prototype")) {
RHS = make_function_from_source_code_string(..right of <|..);
RHS.prototype = {...};
RHS.prototype.__proto__ = LHS.prototype;
RHS.__proto__ = LHS;
}
}
And so "var SubClassConstructor = ClassConstructor <| function () {}"
will maintain the pseudo-clasical-oo-facade that exists in ES currently.
Jay
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
