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Examples that work as expected:

`
Clojure 1.7.0-master-SNAPSHOT
user=> (dissoc {})
{}
user=> (disj #{})

{}

user=> (conj {})
{}
user=> (conj [])
[]
`

Examples that do not work as desired, but are changed by the proposed patch:

`
user=> (assoc {})
ArityException Wrong number of args (1) passed to: core/assoc clojure.lang.AFn.throwArity (AFn.java:429)
user=> (assoc! (transient {}))
ArityException Wrong number of args (1) passed to: core/assoc! clojure.lang.AFn.throwArity (AFn.java:429)
user=> (dissoc! (transient {}))
ArityException Wrong number of args (1) passed to: core/dissoc! clojure.lang.AFn.throwArity (AFn.java:429)

;; patch enables conj! with multiple arguments, like conj
user=> (conj! (transient []) 1 2 3)
ArityException Wrong number of args (4) passed to: core/conj! clojure.lang.AFn.throwArity (AFn.java:429)

;; patch would give error for missing value for last key to assoc!, not silently use nil for last value
user=> (assoc! (transient {}) 1 2 3)

object[clojure.lang.PersistentArrayMap$TransientArrayMap 0x2e7569b8 "clojure.lang.PersistentArrayMap$TransientArrayMap@2e7569b8"]

`

I looked through the rest of the code for similar cases, and found that there were some other differences between them in how different numbers of arguments were handled, such as:

  • conj handles an arbitrary number of arguments, but conj! does not.
  • assoc checks for a final key with no value specified (CLJ-1052), but assoc! did not.

History/discussion: A discussion came up in the Clojure Google group about conj giving an error when taking only a coll as an argument, as opposed to disj which works for this case:

https://groups.google.com/forum/?fromgroups=#!topic/clojure/Z9mFxsTYTqQ

Screened by: Alex Miller

16 Answers

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Reference: https://clojure.atlassian.net/browse/CLJ-1103 (reported by jafingerhut)
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