``` sealed class Operation <out T> { dat...

# announcements

[Syed Faraz]

sealed class Operation <out T> {

   data class InsertOperation<out T>(var insertedData: ArrayList<T>)
}

Hi, this gives type parameter t is declared as 'out' but occurs in 'invariant' position in type t, can anyone tell me what is correct way of handling this type of variance checking?

[diesieben07]

An out parameter means you are only getting values of that type out of the class. But ArrayList permits writing. Use a List<T>, which is not modifiable

[Syed Faraz]

my first thought was that so i have checked using list as well, but it throws the same error unfortunately. is there anything i'm missing here?

[diesieben07]

You also have insertedData declared as a var, which means you can, again, put data in.

[max]

is the second <out T> really necessary?

[Syed Faraz]

@Massimo yes, we need it, otherwise we'll not be able use it,
data class InsertOperation<out T>(val insertedData: List<T>) :Operation<T>
it'll be something like this

[Syed Faraz]

@diesieben07 thanks it's working now.

[max]

@Syed Faraz thanks you're right, in your snippet is the first one to be unused