specialized functions for unknown types

function fieldtype(x::Any)
	T = typeof(x)
	if !isbits(T)
		error(T, " is not a bitstype, so it doesn't have the right memory layout")
	end
	types = T.types
	@assert !isempty(types)
	ftype = types[1]
	if any(t -> t!= ftype, types)
		error("field types are not homogenious for: ", T)
	end
	# We can return the field type, 
	# this means we can make a more specific function for this type
	eval(( :(fieldtype(x::$T) = $ftype) ))
	return ftype
end