Deterministic destruction

Live owned locals drop at lexical scope exit in reverse binding declaration order, with inner scopes before outer scopes. return, ?, break, and continue clean up the scopes they leave. Moving transfers the cleanup obligation; moved or already dropped values are not dropped again. Replacement destroys the previous initialized value before installing the new one; see assignment for evaluation order.

drop(value) -> () consumes an owner early. It cannot destroy a borrowed referent or consume an owner during a conflicting loan. Dropping a shared immutable string releases that owner’s share, without freeing other owners’ storage. Ending a borrow at last use does not move observable resource destruction away from its specified scope exit or explicit drop.

Owned expression temporaries drop at the end of their full expression unless transferred. A block transfers its result before destroying its other locals. Loop conditions and each comprehension iteration finish their own temporaries. An early propagation cleans pending evaluated operands before enclosing scope cleanup; later operands do not run.

A class may declare def __del__(self) -> () (an exclusive receiver) for additional cleanup. The hook runs before automatic field cleanup. It cannot return a recoverable error, yield, allow references to the dying value to escape, or be called as an ordinary method. Because the hook receives every field, fields of such a class cannot move out. Fields clean up automatically, skipping any field that has moved out:

A child finishes destruction before its next sibling begins. Recursive heap cleanup requires no allocation or recursive native stack growth; source-level recursive calls inside user hooks can still use the native stack. User cleanup retains its own effects and allocation costs. Types with custom destruction, including nested fields, cannot be copied. Explicit fallible shutdown should return Result; a destructor provides fallback cleanup rather than reporting shutdown failure.

Bounded-stack destruction does not make a recursive traversal bounded-stack. An explicit descendant cursor or worklist is still needed for unbounded-depth input. See linked-data examples.

Suspended or never-started generators drop their remaining captures and locals without resuming the body. Statements following yield are not cleanup hooks. Resource scopes insert exit calls into ordinary cleanup. Tail transfers finish caller cleanup before entering the callee. Fatal traps and process aborts do not unwind.