Collection (Set) literal syntax should only be used with compile time constants

[sw1nn]

The Collections section should elaborate on when set literal syntax is not appropriate, i.e. when the values in the set are not compile time constants.

There's been recent discussion on this on the Clojure ML[1] and it's spawned a wiki page[2] The consensus is (AFAICT) that if there's a possibility of duplicate values the constructor functions are preferred over literal syntax. There's further discussion on whether duplicates are appropriate in literals, but I don't think that's worth adding here.

I propose adding the following

• Only use set literal notation when set values are compile-time constants

; good
(hash-set (func1) (func2))

; bad, will throw exception if (func1) == (func2)  at runtime.
#{(func1) (func2)}

[1] https://groups.google.com/forum/?fromgroups=#!topic/clojure/AG667ACBd3I
[2] http://dev.clojure.org/display/design/Allow+duplicate+map+keys+and+set+elements

[bbatsov]

Great suggestion. I'd suggest expanding the rule and it's example a bit and sending a PR.