Different question: I want to return 1 if a map's value is not set or am empty list. Is there a more...

# getting-started

[Draget]

Different question:
I want to return 1 if a map's value is not set or am empty list. Is there a more elegant way than:

if (!myMap.containsKey(color) || myMap[color]!!.isEmpty()) return 1

[Milan Hruban]

myMap[color]?.isEmpty() != false

[Draget]

Hmm, okay.

I thought using the ? operator would skip the whole expression (and thus the whole if), if it encountered a null.

But this means it evaluates to something... that is apparently not equal to false?

[Milan Hruban]

using the safe access operator does skip the rest of the expression, if the left side is null. But the if statement is not part of that expression.
with the expression I wrote, you have several cases:
1. The item is not in the map, so you get null?.isEmpty() which evaluates to null, so null != false -> true
2. the item is in the map, but it is empty, so you get theEmptyItem?.isEmpty(), which evaluates to true so true != false -> true
3. the item is in the map and it is not empty, so you get notEmptyItem?.isEmpty(), which evaluates to false so false != false -> false

[Draget]

Ah, so it basically 'evalutes' the expression to null, if any part is null.

So null?.something() == null would be true?

I get it, thanks. 🙂

[Milan Hruban]

yes that would be true:)

[georg]

Just out of interest: Are you working on the Advent of Code puzzles? 🙂

[Draget]

Of course I am. 😛 This piece was for Day07 and I used it here (spoiler).