Often, when you have a compiler-y recursive ADT, you will want to allocate the individual nodes in an arena rather than from the global allocator as with Box. A

Often, when you have a compiler-y recursive ADT, you will want to allocate the individual nodes in an arena rather than from the global allocator as with Box. And at that point, you can use references (with the lifetime of the arena) rather than Boxes, and you can pattern match across those. (Note that this doesn't work if your "arena" is just a Vec, which is something people have sort of hijacked the term "arena" for. It needs to be an arena that doesn't reallocate its contents on growth, something like https://docs.rs/bumpalo/latest/bumpalo/ https://docs.rs/bumpalo/latest/bumpalo/, in order to hand out references that live across allocations like this.)