Existential Operator / Null Propagation Operator

Sander Deryckere sanderd17 at gmail.com
Tue Jun 2 16:05:07 UTC 2015

2015-06-02 17:49 GMT+02:00 Brendan Eich <brendan at mozilla.org>:

> Sander Deryckere wrote:
>> For the prefix operator, it's unclear to me how you would do the
>> following: Say you know `obj` is non-null, you want to test if it has a key
>> `k1`, but if `k1` exists, you know it will also have a key `k2` a level
>> deeper. With the suffix operator, this would be `obj[k1]?[k2]`, but with
>> the prefix operator, it could be `obj?[k1][k2]`
> You circled back to the incompatible syntax, `?[`, but the prefix idea
> would have `?obj[k1][k2]`. The `?` goes in front at the start of an
> operand, and is thus unambiguous with respect to the ternary operator.

The question is not about the existence of `obj`, but if `obj` has a key
`k1`. AFAICS, `?obj[k1][k2]` would test the existence of `obj`, which I
don't need in this example. To test the existence of a key inside `obj`, a
prefix operator should come somewhere before the key.
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