Sealed classes inside another class in Kotlin can't be compiled: cannot access '<init>' it is private : <p>If I used the example from the <a href="https://kotlinlang.org/docs/reference/sealed-classes.html" rel="noreferrer">docs</a>, </p>

<pre><code>class SomeActivity : AppCompatActivity() {
    sealed class Expr
    data class Const(val number: Double) : Expr()
    data class Sum(val e1: Expr, val e2: Expr) : Expr()
    object NotANumber : Expr()
}
</code></pre>

<p>it does not compile, with the error:</p>

<pre><code>Cannot access '&lt;init&gt;', it is private in 'Expr'.
</code></pre>

<p>However, moving it outside the enclosing class makes it compile:</p>

<pre><code>sealed class Expr
data class Const(val number: Double) : Expr()
data class Sum(val e1: Expr, val e2: Expr) : Expr()
object NotANumber : Expr()

class SomeActivity : AppCompatActivity() {
}
</code></pre>

<p>Why is this so? Is this an intended behavior? The docs does not seem to mention this.</p>
