Why can't I instantiate an empty array of a nested class?
This definitely looks like a bug in the compiler, especially as you're allowed to instantiate an empty array of a nested class just fine; it simply doesn't work with the initialiser syntax.
I'll raise a bug. In the meantime, for anyone experiencing the problem, you can work around it by using assignment syntax with an empty array and a specified class for the variable, rather than constructor syntax:
var foobar: [Wrapper.InsideClass] = []
Another way to do is to use Array<T>() constructor.
let arrayOfNestedClass = Array<Wrapper.InsideClass>()