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Why cant nullable arrays/hashmaps be accessed using

When I have a nullable array/list/hashmap such as

var x: ArrayList<String>? = null


I know can access the element at index 1 like so

var element = x?.get(1)


or I could do it in a unsafe way like this

var element = x!![1]


but why can't I do something like this

var element = x?[1]


what's the difference between getting elements from an array using the first example and the last example, and why is the last example not allowed?

1 Answer
1

In the first example, you're using the safe call operator ?. to call the get function with it.

?.

get

In the second example, you're using the operator on the non-nullable return value of the x!! expression, which of course is allowed.

x!!

However, the language simply doesn't have a ? operator, which would be the combination of the two. The other operators offered are also don't have null-safe variants: there's no ?+ or ?&& or anything like that. This is just a design decision by the language creators. (The full list of available operators is here).

?

?+

?&&

If you want to use operators, you need to call them on non-nullable expressions - only functions get the convenience of the safe call operator.

You could also define your own operator as an extension of the nullable type:

operator fun <T> List<T>?.get(index: Int) = this?.get(index)

val x: ArrayList<String>? = null

val second = x[2] // null


This would get you a neater syntax, but it hides the underlying null handling, and might confuse people who don't expect this custom extension on collections.

get

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