How to convert Array<T?>? into Array<T> in Kotlin

Question

I'm taking my first steps in Kotlin, and trying to write a simple string split function. I started with this:

fun splitCSV(s : String) : Array<String> {
    return s.split(",");
}

Which I guess can be also written like this:

fun splitCSV(s : String) : Array<String> = s.split(",");

But I'm getting a type error, since s.split returns an Array<String?>? and not Array<String>. I couldn't find a simple way to do a cast, so I wrote this function to do the conversion:

fun forceNotNull<T>(a : Array<T?>?) : Array<T> {
    return Array<T>(a!!.size, { i -> a!![i]!! });
}

fun splitCSV(s : String) : Array<String> = forceNotNull(s.split(","));

However, now I'm getting a runtime error:

ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String

If I change T in forceNotNull to String, then it works, so I guess I'm close to a solution.

Is this the right way to go about it? And if it is, how can I fix forceNotNull to work in the generic case?

Function sureItemsNotNull already added: youtrack.jetbrains.com/issue/KT-1391 — Stan Kurilin
– Stan Kurilin, Commented Apr 3, 2012 at 21:21
@StasKurilin can you give an example of how that could be used with the above function definition? — tim_yates
– tim_yates, Commented Apr 4, 2012 at 7:55
The exception you are getting is a bug, of course. The easiest solution in this case is just a cast: s.split(",") as Array<String> — Andrey Breslav
– Andrey Breslav, Commented Apr 8, 2012 at 15:13
@Andery I guess the warning "This cast can never succeed" is also a bug. Nice to hear from the authority, thanks! — itsadok
– itsadok, Commented Apr 9, 2012 at 7:14
This should be closed as a duplicate of 33583235. The other question is newer, more direct and answers are for current kotlin 1.0 betas and beyond. — Jayson Minard
– Jayson Minard, Commented Dec 29, 2015 at 5:09

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Not sure it's the best method, but this seems to work:

fun splitCSV(s : String) : Array<String> {
  return ( s.split(",") as? Array<String>? ).sure() ;
}

Although IntelliJ highlights the as? with "This cast can never succeed"... So my initial optimism is fading

Oddly though, it seems to work...

As does:

fun splitCSV(s : String) : Array<String> {
  return s.split(",").sure() as Array<String> ;
}

But with the same warning... I'm getting confused, so I'll stop now :-/

Edit

Of course, you can get it to work with List<String>:

import java.util.List

fun splitCSV(s : String) : List<String> {
  return s.split(",")!!.map<String?,String> { it!! }
}

but that wasn't the question ;-)

edited Jun 20, 2020 at 9:12

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answered Apr 3, 2012 at 12:19

tim_yates

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2 Comments

itsadok Over a year ago

Like Andrey said, the cast is the right approach, so you were very close... Accepting this.

Jayson Minard Over a year ago

Can you update the code here for .sure() to !! since that is outdated code.

mightyWOZ · Accepted Answer · 2021-08-18 16:12:57Z

1

Since the time of this post, kotlin has changed a lot and now there are lot easier and nice(explicit casts should be avoided) ways of converting Array<T?>? to Array<T>, one way would be to do

val data: Array<String?>? = getData()
val notNullArray: Array<String> = data?.filterNotNull()?.toTypedArray() ?: arrayOf()

here we make use of filterNotNull to get a List<String> and then convert that list to an Array<String>, if however the original array is null then we simply use arrayOf(), which given us an empty Array<T>

?: is the elvis operator which returns the expression on its left if its not null otherwise it returns the value of expression on the right

answered Aug 18, 2021 at 16:12

mightyWOZ

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Comments

Rupesh Kumar · Accepted Answer · 2021-08-18 18:16:02Z

0

in Simple way you can cast string to Array in kotlin by:-

fun splitCSV(s: String) = s.split(",").toTypedArray()

call this function by

val array: Array<String> = splitCSV("ABC,XYZ,test,rupesh")

in kotlin CharSequence.split(regex) return List so if you want to change in type Array use .toTypedArray() method

answered Aug 18, 2021 at 18:16

Rupesh Kumar

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