mutable locking.clj

(defprotocol TestProtocol
  (test-method [this]))

(deftype MutableLocking
  ; Compiles ok
  [^{:volatile-mutable true} mut-var]
  TestProtocol
    (test-method [this]
      (locking this
        (set! mut-var {:set true})
        this)))

(deftype MutableLockingFailure
  ; Placing return value outside of locking
  ; Fails to compile, complaining mut-var is not mutable.
  [^{:volatile-mutable true} mut-var]
  TestProtocol
    (test-method [this]
      (locking this
        (set! mut-var {:set true}))
      this))