I still need to ponder this more. Why is indexing an `undef` so bad? It's possible in Base Julia, although it throws an error:

	julia> a = Array(ASCIIString, 5)
	5-element ASCIIString Array:
	 #undef
	 #undef
	 #undef
	 #undef
	 #undef

	julia> a[1]
	ERROR: access to undefined reference
	 in getindex at array.jl:246