Module Comments

Domenic Denicola domenic at domenicdenicola.com
Sat Dec 8 18:51:27 PST 2012


> -----Original Message-----
> From: Andreas Rossberg [mailto:rossberg at google.com]
> Sent: Thursday, December 6, 2012 11:31
> 
> On 6 December 2012 16:44, Domenic Denicola
> <domenic at domenicdenicola.com> wrote:
> > For the record, here's the idea Yehuda and I worked out:
> >
> > https://gist.github.com/1ab3f0daa7b37859ce43
> >
> > I would *really* appreciate if people read it (it's easy reading, I
> > promise!) and incorporated some of our concerns and ideas into their
> > thinking on module syntax.
> 
> However, the more radical parts of your proposal (allowing arbitrary export expressions, and arbitrary import patterns) do not work.
> 
> The problem is that imports are not normal variable assignments. They do not copy values, like normal destructuring, they are aliasing bindings! If you were to allow arbitrary expressions and patterns, then this would imply aliasing of arbitrary object properties. Not only is this a completely new feature, it also is rather questionable -- the aliased location might disappear, because objects are mutable.

Thanks for the feedback Andreas; this is really helpful. It took me a while to figure out what you meant by this, but I think I understand now. However, I think that since the bindings are const bindings, the difference between copying and aliasing is unobservable—is that right? Thus the mental model could be copying in all cases, both top-level and deeper.

I think the symmetry I am looking for is that

import { x: [a, b], f } from "foo";

should work the same as

import foo from "foo";
const { x: [a, b], f } = foo;

And I realize the linked gist does not introduce const bindings, but instead let bindings; that's easy enough to fix if it's the right path forward.

> You could also consider imports always meaning copying, but then you exporting a variable will no longer be useful.

This is the part that made me question whether I understand what you're saying. What do you mean by "exporting a variable" and "useful"?



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