This document summarizes three Clojure functions for updating atoms and refs: reset! sets the value of an atom without regard for its current value and returns the new value; compare-and-set! atomically sets the value of an atom only if its current value matches the given old value, returning true if set or false if not; commute sets the in-transaction value of a ref by applying a function to its current value and commits by applying the function to the last committed value, allowing for more concurrency than ref-set.

1. LDC 14/11/2011

2. 3 clojures funcions
Set - Rearrange
reset!
compare-and-set!
commute

3. user=> (doc reset!)
-------------------------
([atom newval])
Sets the value of atom to newval without regard for the
current value. Returns newval.

4. compare-and-set!
-------------------------
([atom oldval newval])
Atomically sets the value of atom to newval if and only if
the current value of the atom is identical to oldval. Returns
true if set happened, else false

5. commute
-------------------------
([ref fun & args])
Must be called in a transaction. Sets the in-transaction-value of ref
to:
(apply fun in-transaction-value-of-ref args)
and returns the in-transaction-value of ref.
At the commit point of the transaction, sets the value of ref to be:
(apply fun most-recently-committed-value-of-ref args)
Thus fun should be commutative, or, failing that, you must accept
last-one-in-wins behavior. commute allows for more concurrency
than ref-set.

7. partition-*