Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

For the More Curious: The reified Keyword

There are cases where it is useful to know the specific type that is used for a generic parameter. The reified keyword allows you to check a generic parameter’s type.

Suppose that Madrigal is on a quest to collect loot of a specific type. For example, she may want to collect every hat she can get her hands on, ignoring all other types of loot. Here is a takeLootOfType function that attempts to capture that logic:

    class LootBox<out T : Loot>(val contents: T) {
        var isOpen = false
            private set

        fun takeLoot(): T? {
            return contents.takeIf { !isOpen }
                .also { isOpen = true }
        }

        fun <U> takeLootOfType(): U? {
            return if (contents is U) {
                takeLoot() as U
            } else {
                null
            }
        }
        ...
    }

    val lootBox = LootBox.random() ...