A class that encapsulates data, adding ability to know when the data has already been viewed. Useful for putting one-shot events, like "display dialog", into a State object that can be reapplied to a view.

ViewOnceData.kt

import java.util.concurrent.atomic.AtomicBoolean

/**
 * Wraps some data that should track when it has been viewed and allow future viewers to avoid a second showing.
 * Useful for showing messages in the app that auto-hide because this class can exist in the app's state.
 */
data class ViewOnceData<T>(private val data: T) {
    val wasViewed = AtomicBoolean(false)

    /**
     * Returns the data if it has not been viewed before and marks it as viewed.
     * If it has been previously viewed, returns null.
     */
    fun getDataIfNotViewed(): T? {
        return if (wasViewed.compareAndSet(false, true)) {
            data
        } else {
            null
        }
    }

    /**
     * Returns the data regardless of viewed status.
     */
    fun peek() = data
}