IIRC The Rust compiler just uses Cell<&’a> for child terms, which is a somewhat lighter weight solution that still allows mutation. Edit: Either I remembered w

IIRC The Rust compiler just uses Cell<&’a> for child terms, which is a somewhat lighter weight solution that still allows mutation. Edit: Either I remembered wrong or it's changed. Now it uses some kind of custom wrapper around Box: https://github.com/rust-lang/rust/blob/master/compiler/rustc_ast/src/ptr.rs https://github.com/rust-lang/rust/blob/master/compiler/rustc... So actually, the Rust compiler itself uses owned children in its AST!