Protocols don't support varargs. You've defined a protocol with two
methods named say: one takes one argument named a, the other takes
three arguments named a, &, and b.
Protocols are for describing a very minimal set of functionality
needed to implement some richer feature set; the idea is that you
define a Say protocol that is capable of saying things in some basic
sense, and then build a library of functions that operate on Sayable
objects, providing the nice syntactical sugar in the library of real
functions, not in the protocol itself. If you want a say function that
behaves totally differently depending on how many arguments it's
passed (which seems kinda silly, but I'll assume that it's a contrived
example), you could do something more like this:
(defprotocol Say
(say [this args]))
(defrecord Robot []
Say
(say [this args]
(let [[a & [b]] args]
(println (or b (str "hello, " a))))))
(defn make-something-talk [obj & args]
(say obj args))
On Jan 19, 8:02 pm, dennis <killme2...@gmail.com> wrote:
> I have defined a protocol with overload methods,and one has varargs:
>
> (ns test)
> (defprotocol Say
> (say [this a] [this a & b] "say hello"))
> (defrecord Robot []
> Say
> (say [this a] (println (str "hello," a)))
> (say [this a & b] (println b)))
>
> Then ,i new a robot and say something:
> (let [ r (Robot.)]
> (say r "dennis"))
>
> It worked and print "hello,dennis",but if i passed more than one
> arguments,it failed:
>
> (let [ r (Robot.)]
> (say r "dennis" "zhuang"))
>
> and threw exception
>
> java.lang.IllegalArgumentException: No single method: say of
> interface: test.Say found for function: say of protocol: Say (test.clj:
> 9)
>
> It seems that clojure find methods in protocol both by name and
> arity,and in this situation it found more than one methods named
> "say".
>
> I don't know how to solve this problem,any suggestion? thanks a lot.
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