CODEWITHSUNDEEP
genericskotlin
itsadok
itsadok

Reputation: 29342

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

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?

Upvotes: 4

Views: 2334

Answers (3)

Rupesh Kumar
Rupesh Kumar

Reputation: 53

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

Upvotes: 0

mightyWOZ
mightyWOZ

Reputation: 8355

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

Upvotes: 1

tim_yates
tim_yates

Reputation: 171194

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 ;-)

Upvotes: 1

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