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kotlinlang

Hi often find myself having a mutableMap where the values are mutable collections, and so I created this extension :
```fun &lt;K, V&gt; MutableMap&lt;K,V&gt;.getOrCreate(key : K, create : ()-&gt;V?) : V? {
    return if (containsKey(key) ) {
        get(key)
    } else {
        put(key, create())
    }
}```

You have `getOrDefault` and `getOrPut` in the stdlib for exactly that. :slightly_smiling_face: 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. :wink:

Getting into the source code, It'd be also nice to have a `getOrPutImplicitDefault` :slightly_smiling_face:

That way I could create the mutableMap `.withDefault()` and avoid passing the lambda each time

You can add that through an extension function. :wink:

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?