new instantiation design alternatives

Allen Wirfs-Brock allen at wirfs-brock.com
Tue Sep 16 16:48:53 PDT 2014


On Sep 16, 2014, at 12:57 PM, Brendan Eich wrote:

> Allen Wirfs-Brock wrote:
>> We have long standing consensus on the current ES6 class design and that includes a `super()` constructor call that can be arbitrarily placed within the constructor body.
> 
> I'm ok with consensus if it's real and strong. We aren't there yet, and AFAIK we never had cow-path-based use-cases for super calls tucked into the middle of constructors. We definitely had concerns about uninitialized objects, and people wanted to deal with constructor called as function. But conditional super()? I don't remember that.

The ES6 max-min class and @@create instantiation proposals have always allowed arbitrarily placed `super` calls in methods (and up until the recent discussions) we treated class constructors as just the `constructor` method of the class prototype. The cow path for arbitrarily placed method super` is well paved and supports the fully generality of before, after, and around specialization in over-riding subclass methods without requiring additional syntactic affordance. It's a cow path that is about as old as OO programming and is just as applicable to constructor methods as to any other kind of method.

We've also always had conditional super calls, eg: `if (cond) super();` has been valid in any method, including constructors.

But as you say , the real issue we are trying to address now is eliminating exposure of uninitialized non-ordinary objects and support for  constructors called as functions.  I think we're on a good path to solve those. Unfortunately, I think the super in function header discussion is mostly a distraction and not really helping focus the discussion on  the core issues.

Allen




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