Can Clojure's protocol functions be variadic like ordinary functions?

Question

With clojure functions, I can define:

(defn f [x & xs] (apply some-function x xs))

I'm attempting to do this same sort of thing with a protocol, e.g.

(defprotocol foo
  (bar [f])
  (baz [f & gs]))

This compiles (at least in the REPL), but any implementing type seems to fail on this (the variadic, baz) method. Is this officially not supported? The sources that I've consulted are silent.

score 12 · Accepted Answer · answered Mar 23 '11 at 15:58

12

This is not supported, for the reasons Stuart Sierra gives. To go into a little more detail, the & symbol is special only in a destructuring context like let or function arguments. As Stuart makes clear, defprotocol is not such a context.

But & is still a legal symbol, so you've defined a protocol with two functions: bar takes one argument, named f, and baz takes three, named f, &, and gs.

answered Mar 23 '11 at 15:58

amalloy

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FYI, there is a jira issue to flag the use of & in this context as an error. http://dev.clojure.org/jira/browse/CLJ-888 – Alex Miller Feb 05 '14 at 20:22

score 10 · Answer 2 · answered Mar 23 '11 at 07:50

10

As answered Stuart Sierra in following thread, variadic methods aren't supported, and possibly will not supported in the future

answered Mar 23 '11 at 07:50

Alex Ott

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Can Clojure's protocol functions be variadic like ordinary functions?

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