[johncolanduoni]

Inherited mutability and no aliasing mean cyclical structures tend to be a fairly complicated mess of RefCell/Cells. The borrow checker is very good at handling ordered lifetimes but cannot handle more complicated access patterns without the runtime checks in RefCells.

There are graph libraries, but these only help with structures that are graphs in the strict sense (all edges are created equal and not actually part of the structure) as opposed to structs with one or more fields that reference (and have shared ownership of) another node in the graph.