Using generic type of interface in method

Question

I'm getting confused with generics in Kotlin. How can I use T type of Class in function parameters (in addNewItem() and deleteItem())? I'm getting error "Type parameter T is declared as 'out' but occurs in 'in' position kotlin"

interface IStorageManager<out T: IFileItem> { fun getAllItems(): List<T> fun addNewItem(itemToAdd: T) fun deleteItem(itemToDelete: T) }

screen

s1m0nw1 · Accepted Answer · 2018-08-17 19:30:42Z

If your interface only produces T, you can make this clear to the compiler by annotating it with out. In your example you also have methods that act as consumers of T, thus out does not work. Just remove the out keyword and all will work fine.

This is a good reference: https://kotlinlang.org/docs/reference/generics.html

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