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kotlinlang

would be nice if range checks caused smart casting:

```
if (pin?.length != 36) throw Exception()
// pin is smart cast here
```
```
if (pin?.length !in (8..36)) throw Exception()
// pin is not smart cast here
```

Are you sure the latter is legal? It should be calling `operator fun contains(value: Int)`

there is a version of contains with nullable parameter in the stdlib

Moreover, I think just doing `x == null || x ...` is way more readable

If contracts were allowed for operator functions (not sure why not...?), this could be solved easily by adding the following:
```
contract {
  returns(true) implies(element != null)
}
```

Perhaps because operator functions are quite implicit

So having some smart cast that depends on which exact function was resolved might be fragile