Operator overloading for non-value objects
Brendan Eich
brendan at mozilla.com
Tue Jan 14 17:37:04 PST 2014
Kevin Smith wrote:
> What about:
>
> 0L == "0"
So glad you asked, and you will like the answer:
js> 0L == "0"
typein:2:0 TypeError: no operator function found for ==
See
http://image.slidesharecdn.com/jsresp-130914140214-phpapp02/95/slide-12-638.jpg?1379296961,
For the expression v + u
1. Let p = v.[[Get]](@@ADD)
2. If p is not a Set, throw a TypeError
3. Let q = u.[[Get]](@@ADD_R)
4. If q is not a Set, throw a TypeError
5. Let r = p intersect q
6. If r.size != 1 throw a TypeError
7. Let f = r[0]; if f is not a function, throw
8. Evaluate f(v, u) and return the result
If v or u is a string, no handed-operator-symbol-named set on prototype
chain.
> How is "===" defined for user-defined value types? In terms of the T
> == T overload?
You did not read
http://image.slidesharecdn.com/jsresp-130914140214-phpapp02/95/slide-9-638.jpg?1379296961
:-(.
Strict Equality Operators
* The strict equality operators, === and !==, cannot be overloaded
* They work on frozen-by-definition value objects via a structural
recursive strict equality test (beware, NaN !== NaN)
* Same-object-reference remains a fast-path optimization
/be
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20140114/5fd47543/attachment.html>
More information about the es-discuss
mailing list