Create array as [1, 2, 3] and maps as { a: 10 }

1

Just wondering if there’re any plans to introduce a human way to create collections? Something like [1, 2, 3] and maps as { a: 10 }.

I believe the reason they weren’t introduced originally, because it was not clear how to do it in a proper way.

Kotlin development started 11 years ago, in 2010. How many more years kotlin dev team needs to solve this immensely complicated challenge?

2

It is called collection literals, and you should probably watch this video for discussion.

Personally, I do not see how [1,2,3] is be better than List(1,2,3). When I just started to work in kotlin (after groovy), I was advocating for collection literals, but after four years, I changed my perspective and now I do not see any viable reasons to introduce them.

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3

By saying [1, 2, 3] which one do you mean exactly?

listOf(1, 2, 3)
mutableListOf(1, 2, 3)
arrayOf(1, 2, 3)
arrayListOf(1, 2, 3)

I think current solution is better, because it is explicit what kind of data structure we need to create.

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4

By saying [1, 2, 3] which one do you mean exactly?

Possible solutions could be

  1. infer type val list: List<Int> = [1, 2, 3]
  2. For val list = [1, 2] collect usage stats over top 100 kotlin projects on github and see what’s used the most frequently. If you want something else do val list = [1, 2, 3].toMutableList() or use old way val list = mutableListOf(1, 2, 3).

The thing is - you lose nothing, if you wish you can just ignore this literal syntax and continue to use whateverOf(1, 2, 3). But people who like this syntax could use it.

5

My personal opinion is that the current solution is better than both of your suggestions. But as I said, this is just an opinion.

Anyway, the case here is not that this feature is missing, but it was designed in a different way than you expect.

6

Also, it seems this is actually planned for future versions of Kotlin. It is/was discussed here and here. It takes years already for arguing on what would be the best design for this proposal :wink:

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7

The current collection literal proposal makes sense in conjunction with the tuple builders proposal, but not as a stand-alone feature.

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