Android Programming: The Big Nerd Ranch Guide, 5th Edition

State Hoisting

For your Coda Pizza app, you want the PLACE ORDER button to display the price of a pizza based on its toppings: A plain cheese pizza costs $9.99, and each topping adds $1.00 for the whole pizza or $0.50 for half the pizza. Define a computed property called price on your Pizza class to keep track of this price information.

Listing 27.10  Pricing pizzas (Pizza.kt)

import com.bignerdranch.android.codapizza.model.ToppingPlacement.*

data class Pizza(
    val toppings: Map<Topping, ToppingPlacement> = emptyMap()
) {
    val price: Double
        get() = 9.99 + toppings.asSequence()
            .sumOf { (_, toppingPlacement) ->
                when (toppingPlacement) {
                    Left, Right -> 0.5
                    All -> 1.0
                }
            }
    ...
}

Make sure you import your Left, Right, and All ToppingPlacement ...