That lambdas problem got me thinking: Are there other kinds of types that are only visible in a limited scope, for a single execution, but could creep out of that scope? Well, local inner classes (classes declared inside of a method) have limited scope. And if it is a generic method, then we also get a type variable that's assumed to only represent a type for one execution of that method. A problem exploiting that is that you can only have one execution of the method in scope at a time, and if it moves out of scope we lose the type information. But unlike capture types these types have names, so we can restore the type information with a cast.