Kotlin Array init function

Question

I'm new to Kotlin and have difficulty understanding how the init function works in context of an Array. Specifically, if I'm trying to make an array of String type using:

val a = Array<String>(a_size){"n = $it"}

This works, but what does "n = $it" mean? This doesn't look like the init function as it is within curly braces and not inside the parenthesis.
If I want an Array of Int what would the init function or the part inside the curly braces look like?

nhaarman · Accepted Answer · 2017-06-02 11:15:03Z

12

You're calling a constructor with an initializer:

/**
 * Creates a new array with the specified [size], where each element is calculated by calling the specified
 * [init] function. The [init] function returns an array element given its index.
 */
public inline constructor(size: Int, init: (Int) -> T)

Thus, you're passing a function to the constructor which will get called for each element. The result of a will be

[
  "n = 0",
  "n = 1",
  ...,
  "n = $a_size"
]

If you just want to create an array with all 0 values, do it like so:

val a = Array<Int>(a_size) { 0 }

Alternatively, you can create arrays in the following way:

val a = arrayOf("a", "b", "c")
val b = intArrayOf(1, 2, 3)

edited Jun 2, 2017 at 11:15

answered Jun 2, 2017 at 9:37

nhaarman

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4 Comments

Araf Over a year ago

What if I don't want to initialize the Array with any values? Kotlin equivalent of this Java snippet ArrayList<Integer> lst = new ArrayList<Integer>(10);

nhaarman Over a year ago

In Java this will result in a list with all 0 values. In Kotlin you will have to specify this explicitly.

Araf Over a year ago

I see. But I'm in the process of writing a twig template and I'm trying to generalize the array creation syntax for various datatypes. So I want something that reads, Array<{{TYPE}}>(a_size) { {{GENERAL_INITIALIZER}} }. Is this possible with the current syntax?

nhaarman Over a year ago

You will either need to create an array with nullable values, or provide a default non-null value for the type.

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