Also reader macro: @ref/@agent/@var/@atom/@delay/@future/@promise. Within a transaction, returns the in-transaction-value of ref, else returns the most-recently-committed value of ref. When applied to a var, agent or atom, returns its current state. When applied to a delay, forces it if not already forced. When applied to a future, will block if computation not complete. When applied to a promise, will block until a value is delivered. The variant taking a timeout can be used for blocking references (futures and promises), and will return timeout-val if the timeout (in milliseconds) is reached before a value is available. See also - realized?.