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kotlinlang

Question about extension properties. This is the given example:
```
val &lt;T&gt; List&lt;T&gt;.lastIndex: Int
    get() = size - 1
```
And this text:
&gt; Note that, since extensions do not actually insert members into classes, there's no efficient way for an extension property to have a backing field. This is why initializers are not allowed for extension properties. Their behavior can only be defined by explicitly providing getters/setters.

So if I'm reading this right, I can't actually store some value in an extension property, but rather it's a way of wrapping some custom functionality in the form of a property for convenience?