set!

(set! field value)

Assigns a deftype field marked ^:unsynchronized-mutable or ^:volatile-mutable, inside the type's own inline methods, answering the value. A closure created in the method copies the field when created, so a set! inside one is refused.

A ^:dynamic var bound by an enclosing binding assigns the same way: the write sets the thread-local value and answers it, even from a function called inside the binding. Outside any binding it signals Can't change/establish root binding of: ... with set at run time, after the value evaluates -- the same error a non-dynamic global's set! signals. The clojure.core specials assign the same way (*out*, *err*, *print-dup*, ...), except the flags clojure.main binds around a script (*warn-on-reflection*, *unchecked-math*, *print-length*, *print-level*, *assert*, ...): those are always bound, so set! assigns them anywhere, like the oracle -- *ns*, *file* and *1 included. *repl* is bound only in the REPL.

Any other target is refused like the oracle: a local, a parameter or an immutable field with Cannot assign to non-mutable: ...; a host field is not supported yet (the java: surface has no field write).

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