conj

(conj coll x ...)

Answers a fresh collection with the values added, per kind: a member onto a set, an entry onto a map, at the end of a vector, at the front of a list -- nil collects like a list. A set or a seq (strict or lazy) conjoined onto a map contributes its members as entries (two-member vectors), a sorted map its pairs and a Java Map its entries (interpreter and JVM); a list of non-entries, including a (k v) one, is no entry and signals, like anything else conjoined onto a map. Entries conjoined onto a record keep the type; onto an atom (or a ref/agent/volatile, the same cell), a deftype or reify it signals, like the oracle.

As a value a collection plus a rest list of items, folded one by one -- so alter and swap! over conj run what a call would run. With no arguments [], the init arity transduce calls.

Deviation: transients (conj!) are refused by name.