Nice to know that 
I think it’s because I manually define List as a small union and not an abstract type.
The linked list implementation in DataStructures.jl seems very basic, without much care about optimization. I guess it’s not widely used, otherwise there’d be something more clever.
How do you plan using allocators with dynamically changed nodes? E.g. when a node is deleted, or a new one added inbetween the existing etc.