ruby-ast 2.4.1-1 (amd64 binary) in ubuntu noble

 ast embraces immutability; each AST node is inherently frozen at
 creation, and updating a child node requires recreating that node
 and its every parent, recursively.
 .
 This is a design choice. It does create some pressure on
 garbage collector, but completely eliminates all concurrency
 and aliasing problems.
 .
 See also AST::Node, AST::Processor::Mixin and AST::Sexp classes for
 additional recommendations and design patterns.