After review, several seq functions from clojure-contrib have been
promoted to clojure [1], [2], [3]. Hopefully the FAQ below will answer
the major questions you may have:
1. Is this a breaking change to Clojure?
No. Rich is super-careful to grow Clojure by expansion, not by
breaking change.
2. Is this a breaking change to Contrib?
Yes. Contrib is a community-contribution area. Part of its mission is
to germinate ideas that may get promoted to Clojure, and when that
happens contrib users will have to adapt. Usually this will simply
mean removing a require/use, or changing a fn name.
3. Why did some of the fn names change?
Because they were bad names. :-) Clojure is careful to encourage the
use of fns that will have good performance characteristics, and make
it obvious which fns are "seq-y" (therefore O(n)). rand-elt became
rand-nth to make it clear that its performance is bound to the
performance of nth on the underlying collection. Similarly, includes?
became seq-contains? to make clear that the fn must walk the sequence.
Avoid seq-contains? when you have a set or map!
4. Why did some semantics change?
Because they were not the most generally-desirable semantics. The
contrib group-by returned a sorted map, when in most cases sorting is
overkill, so the new core fn returns a plain ol' map.
5. Couldn't you have left the old fns in place in contrib, to avoid
breakage?
No, for multiple reasons. Name collisions are one. But the bigger one
is that the fns in core have been audited by Rich for performance and
correctness. Leaving the old fns in contrib would be a recipe for
lower-performing (or even, in rare cases, buggy) programs.
6. Why did this break my project?
Hopefully it doesn't. But, it seems that a lot of people are tracking
their apps (via leiningen or maven) to build snapshots of both Clojure
and Contrib. This is a risky development practice, particularly in the
case of Contrib. As a community, we need to develop a saner way to
stay near the edge without being right on it.
7. How do I fix it?
Your code gets smaller. Remove requires or uses that refer to promoted
fns. You already have them in core! For the fns whose names have
changed, update the names in your code.
Comments and questions welcome!
Stu
[1]
https://www.assembla.com/spaces/clojure/tickets/312-audit---promote-some-clojure-contrib-seq-fns
[2]
http://github.com/richhickey/clojure/tree/a55df92faa0c51c634d93a8d991ccfd2638b108b
[3]
http://github.com/richhickey/clojure-contrib/commit/78ee9b3e64c5ac6082fb223fc79292175e8e4f0c
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