On Mar 24, 2012, at 5:54 PM, Allen Wirfs-Brock wrote:
> I primarily favor sticking with "constructor" because the
> safety/maximally-miminal proposal is all about being conservative...
I think you'll find what I'm saying is as conservative as what you've been
advocating. Your reply demonstrates that we've been talking past each other.
>> a) spell it "new" -- ergonomics trumps corner cases; hard cases make bad
>> law
> deviates from chapters 13 and 15.
>
> (class () {}) isn't interchangeable with (function () {}). Shouldn't it be?
When I say "spell it 'new'" I mean "the *surface syntax* is spelled 'new'".
That has nothing to do with the semantics. The semantics is described in point
b). Keep reading...
>> b) desugar it to the constructor function and the p.constructor property
>> only
>
> but presumably means that an instance method named new can't be defined using
> a class definition.
Not with the declarative syntax, no. But easily enough imperatively:
class C { new(x) { this.x = x } } // defines C.prototype.constructor === C
C.prototype.new = function() { console.log("I am C's 'new' method") }
Notice the comment: the class definition uses 'new' for the surface syntax, but
that defines C.prototype.constructor, *not* C.prototype.new. If you want to add
a prototype method called 'new', you can do that imperatively, the same old way
as ever in JS.
> Or, perhaps only if "new" is explicitly string quoted as a property name.
> "new" is not a totally unreasonable method name. Also presumably means that
> defining an instance method named constructor is disallowed.
That's true, "new" is not an unreasonable method name. It's still a rare method
name. Syntax is about optimizing for common cases. With my proposed syntax, you
don't have a declarative way to create a prototype method called "new" but you
still have an imperative way to do it, the same old way as before.
>> c) i.e., don't create a p.new property -- no more prototype pollution
>> please
>
> I presume you mean it also doesn't define a p.constructor property. This has
> similar problems to a).
No, no, see b) -- it *does* define a p.constructor property!
What I've been trying to explain is that we can use "new" for the *surface
syntax* but desugar it just the same as the "constructor" version: the
constructor becomes both the value of the class and the p.constructor property.
> It deviates from the legacy ES "class model"
It implements *exactly* the legacy ES class model.
> Also, most instance inherit from Object.prototype so they will still have an
> inherited "constructor" property whose value is Object.
They will not, because p.constructor is the constructor.
> A very common idiom is to query the "class" of an object. Just look how
> frequently you see could like p.class in Java or Ruby code or( p class) in
> Smalltalk code. Thew equivalent of this using ES chapter 13/`5 objects is
> p.constructor. Which would you prefer to see in future ES code
> p.constructor===q.constructor or p.new===q.new
My proposal is not, and has never been, to change the C.prototype.constructor
idiom. It is to choose a different surface syntax that desugars to *exactly*
the classic idiom.
Dave
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