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[CLJ-1103] Make conj assoc dissoc and transient versions handle args similarly Created: 04/Nov/12  Updated: 29/Aug/14

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.4, Release 1.5, Release 1.6
Fix Version/s: None

Type: Enhancement Priority: Minor
Reporter: Andy Fingerhut Assignee: Unassigned
Resolution: Unresolved Votes: 6
Labels: None

Attachments: File clj-1103-6.diff    
Patch: Code and Test

 Description   

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)

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



 Comments   
Comment by Andy Fingerhut [ 04/Nov/12 6:04 PM ]

clj-1103-make-conj-assoc-dissoc-handle-args-similarly-v1.txt dated Nov 4 2012 makes conj conj! assoc assoc! dissoc dissoc! handle args similarly to each other.

Comment by Brandon Bloom [ 09/Dec/12 5:30 PM ]

I too ran into this and started an additional discussion here: https://groups.google.com/d/topic/clojure-dev/wL5hllfhw4M/discussion

In particular, I don't buy the argument that (into coll xs) is sufficient, since into implies conj and there isn't an terse and idiomatic way to write (into map (parition 2 keyvals))

So +1 from me

Comment by Andy Fingerhut [ 08/Nov/13 10:41 AM ]

Patch clj-1103-2.diff is identical to the previous patch clj-1103-make-conj-assoc-dissoc-handle-args-similarly-v1.txt except it applies cleanly to latest master. The only changes were some changed context lines in a test file.

Comment by Andy Fingerhut [ 23/Nov/13 12:52 AM ]

Patch clj-1103-3.diff is identical to the patch clj-1103-2.diff, except it applies cleanly to latest master. The only changes were some doc strings for assoc! and dissoc! in the context lines of the patch.

Comment by Andy Fingerhut [ 14/Feb/14 12:04 PM ]

Patch clj-1103-4.diff is identical to the previous clj-1103-3.diff, except it updates some context lines so that it applies cleanly to latest Clojure master as of today.

Comment by Alex Miller [ 05/Jun/14 9:29 PM ]

Can someone update the description with some code examples? Or drop them here at least?

Comment by Brandon Bloom [ 05/Jun/14 9:35 PM ]

What do you mean code examples?

These currently work as expected:
(dissoc {})
(disj #{})

The following fail with arity errors:
(assoc {})
(conj {})

Similarly for the transient ! versions.

This is annoying if you ever try to do (apply assoc m keyvals)... it works at first glance, but then one day, bamn! Runtime error because you tried to give it an empty sequence of keyvals.

Comment by Andy Fingerhut [ 06/Aug/14 5:05 PM ]

Patch clj-1103-5.diff dated Aug 6 2014 applies cleanly to latest Clojure master as of today, whereas the previous patch did not. Rich added 1-arg version of conj to 1.7.0-alpha1, so that change no longer is part of this patch.

Comment by Andy Fingerhut [ 29/Aug/14 6:04 PM ]

Patch clj-1103-6.diff dated Aug 29 2014 is identical to the former patch clj-1103-5.diff (which will be deleted), except it applies cleanly to the latest Clojure master.

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