CODEWITHSUNDEEP
kotlinexceptionmutablelist
Pranesh Kandasamy
Pranesh Kandasamy

Reputation: 11

when used .remove function of mutable List compiler throws exception any alternative?

This gives Exception in thread "main":

java.lang.UnsupportedOperationException: remove

fun main(args: Array<String>) {
   val list = listOf(0, 1, 2, 3, 4, 5, 6, 7, 8);
   var record: MutableList<Int>;
   record = list as MutableList<Int>;
   record.remove(2);
   print(record);
}

Upvotes: 0

Views: 753

Answers (2)

Tenfour04
Tenfour04

Reputation: 93609

Casting does not change an object into a different kind of object. When you assign list to record, it is still a read-only List, but you've forced the compiler to treat it like a MutableList, so it will fail at runtime instead of compile time.

Since you instantiate list as a read-only List, it is protected from changes (at least to its size). If that is not what you want, you should instantiate it as a MutableList to begin with. Or if you just need a copy of it that you can change, you can use toMutableList() to get a copy.

Upvotes: 3

jeprubio
jeprubio

Reputation: 18002

You should use .toMutableList() to copy the list in a new mutable list:

val list = listOf(0, 1, 2, 3, 4, 5, 6, 7, 8)
val record = list.toMutableList()
record.remove(2)
print(record)

This outputs:

[0, 1, 3, 4, 5, 6, 7, 8]

Upvotes: 1

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