Existential Operator / Null Propagation Operator

Brendan Eich brendan at mozilla.org
Tue Jun 2 15:49:59 UTC 2015

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.


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