[Proposal] New syntax for lazy getters

[Augusto Moura]

I don't think a new keyword is the right path here. For classes lazy fields
can easily be implemented via decorators in the last proposal[1] (also,
Groovy has previous work implementing a `@Lazy` annotation[2] with AST
transformations for the same use case). In code something like:
``` js
const lazy = (fieldMetadata) => {
  // change the field value in descriptor to a lazy factory
};

class Foo {

  @lazy bar = slowCalculation();

  @lazy statements = (() => {
     if (this.bar > 0) {
       return fooify();
     } else {
       return barify();
     }
  }());

}
```

What it's doesn't cover (and in my opinion should be the focus of a new
proposal) is Decorators for literal objects. Something like the code below
is yet not proposed:

``` js
const foo = {
  @lazy bar: 3,
};
```

I didn't made a deep search in ESDiscuss history but I remember this
feature being mentioned sometime ago.

[1]: https://github.com/tc39/proposal-decorators
[2]: http://groovy-lang.org/metaprogramming.html#xform-Lazy
-- 
Augusto Moura
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