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kotlinlang

Here's a quirk of sealed classes I found while testing - given `sealed class PostGeneration`, implemented by `class Error : PostGeneration() ` and `class Post : PostGeneration()`, and a call to a method which returns `PostGeneration`, the compiler naturally enough doesn't know if it's a `Post` or an `Error`. But as soon as I introduce a new variable through a cast, the compiler now knows the class of the result of the function call:
```
	val result = Post.Builder.createPost(fileName,mDocument,project)
	val isPost = result is Post
	assertTrue(isPost)

	val post = result as Post            // _if I comment this out, then result.tags is undefined and the compiler rejects it. But I don't need to use this "post" variable so long as it is defined. Defining "post" is enough for the compiler to know what to do with "result"._
	assertEquals(1,result.tags.size)
	assertEquals("aTag",post.tags[0])
```