Type mismatch error when adding a map value to a variable (Kotlin)

Question

1. I want to add a value from a MutableMap to the total, but I keep getting Type mismatch: inferred type is Int? but Int was expected error and I don't know how to fix this issue

2. I tried calling the value as Int menu[item].toInt() and setting logic in the if statement that checks that the item is indeed Int, but nothing helped.

Please, see the code below

fun main() {
    
    val order = Order()
    order.placeOrder("Noodles")

}


 val menu: MutableMap<String, Int> = mutableMapOf("Noodles" to 10,
                              "Vegetables Chef's Choice" to 5,
                              )

class Order {
    var total = 0

    fun placeOrder(vararg orderedItems: String) {
        for (item in orderedItems) {
            if (item in menu) {
                total += menu[item]
            }
        }
    }
}

Answer 1

Your call to menu[item] is a shorthand for menu.get(item) which is defined as Map<K, out V>.get(key: K): V?.

In case no element with the specified key is found in the map, null is returned.

You may fix this by providing a default value, in case the returned value is null, e.g.:

total += menu[item] ?: 0

Map<K, out V> also provides alternatives, which provide Int instead of Int?. You may use getValue(key: K): V, which throws an NoSuchElementException, when there is no element with the given key. Alternatively, you can utilize getOrElse(key: K, defaultValue: () -> V): V or getOrDefault(key: K, defaultValue: V): V which both provide a fallback value instead of null.

Examples for the different alternatives below:

total += menu.getValue(item)
total += menu.getOrElse(item) { 0 }
total += menu.getOrDefault(item, 0)