[tomp]

I just tested the Fingertree implementation from org.functionaljava

Conclusion: unusuably slow (which kind-of makes sense, since it looks like the common implementation is a 2-3 fingertree - compared to a branching factor of 32 for Vector).

[xscott]

There are lots of implementation details that can make some version slower or faster.

In my own, I use 2..5 branching because a sequence of appends on the front or back will tend to create a tree with 3 pointers per node (when you're about to hit 6, you split. If you get to 1, merge with a neighbor, etc...). Three is close to e, which is optimal in some sense for some operations.

I'm not a Java guy. For my use, having 32 way branching is pretty expensive because I use reference counting for each of the nodes. Since you have a true garbage collector, you don't have that cost, and it wouldn't be difficult to make a 2-32 way implementation.

Anyways, it sounds like you're not impressed and not interested. That's fine :-)