Hi often find myself having a mutableMap where the values are mutable collections, and so I created this extension :

fun <K, V> MutableMap<K,V>.getOrCreate(key : K, create : ()->V?) : V? {
    return if (containsKey(key) ) {
        get(key)
    } else {
        put(key, create())
    }
}

You have

getOrDefault

and

getOrPut

in the stdlib for exactly that. 🙂 The only difference in your example is that your

create

function is allowed to create something that is nullable and (naturally) your function is allowed to return something nullable. However, your map does not necessarily allow that. I recommend the stdlib variants. 😉

thanks 🙂

You can add that through an extension function. 😉

The return value of

put

is the previous value in the map. In your case this is always null. Is that expected in your code?