Try making internal pointers inside Nodes unique_ptrs.

[matsen]

Try making internal pointers inside Nodes unique_ptrs.

[matsen]

Make traversals in terms of const references?

[matsen]

Is this worth it? This will make detrifurcation more difficult.

... the bottleneck is likelihood computation, so the overhead of lots of shared pointers is minimal...

[matsen]

We clearly can't just replace shared_ptr with weak_ptr. It also won't work to have a plain Node as what we pass about, because then if we want the same tree two places, then that will violate unique_ptr.