[int0x80]

There is one common pattern which is required in many use cases when working and representing ASTs - having a `parent` node, or having access to parents and children. This complicates ownership implementation.

Additonally, is essential to provide an API to transform trees or even construct new ones using immutable ASTs like implemented in many compilers eg .NET Roslin or typescript TSC.

[Rusky]

Roslyn specifically does not include parent pointers in its immutable AST nodes. It must do this in order to share those nodes between different versions of the tree.

It only introduces parent pointers in a convenience wrapper layer, built on-demand as you traverse the tree - you could equivalently just pass the parent down as an argument to your tree walking functions.

(The ownership problem of parent pointers also goes away when you use the arena allocation approach that the post arrives at.)