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kotlinlang

Hi guys! I have a question about extension functions.
I declare something like 
```class BaseActivity : AppCompatActivity() {
    fun AppCompatActivity.shortToast(message: String) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
    }
}
```
Why can't I use shortToast inside fragment even with casting to special class like below?
```
(activity as BaseActivity).shortToast("A")	
```
I know that it possible to create function in package scope and use it,  but how to use function declared inside the class?