assoc!

(assoc! tr k v & kvs)

Sets each key of the transient map, or each index of the transient vector, in place and answers tr; a missing last value is nil, like the oracle's. A vector index equal to the count appends; any other out of range is the oracle's IndexOutOfBoundsException, a key that is no integer its IllegalArgumentException. A transient set is refused. As a value a function of the same arguments.