在Clojure中使用defprotocol和defrecord的休息参数有什么问题?

时间:2011-11-14 09:20:42

标签: clojure variadic-functions

下面在Clojure中使用defprotocol和defrecord的休息参数有什么问题?

(defprotocol prot
  (f [this] [this & rest]))

(defrecord rec []
  prot
  (f [this] "one arg")
  (f [this & rest] "more than one arg"))

(prn (f (rec.)))
; (prn (f (rec.) 5))
(prn (f (rec.) 5 6))
; (prn (f (rec.) 5 6 7))

上面的代码打印出我期望的输出:

"one arg"
"more than one arg"

但如果我取消注释任何一个注释行,我会得到以下异常:

Exception in thread "main" java.lang.IllegalArgumentException: No single method: f of interface: user.prot found for function: f of protocol: prot (bug.clj:10)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5376)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.analyze(Compiler.java:5151)
    at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3057)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5371)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.analyze(Compiler.java:5151)
    at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:4670)
    at clojure.lang.Compiler$FnMethod.parse(Compiler.java:4328)
    at clojure.lang.Compiler$FnExpr.parse(Compiler.java:3173)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5367)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.eval(Compiler.java:5421)
    at clojure.lang.Compiler.load(Compiler.java:5857)
    at clojure.lang.RT.loadResourceScript(RT.java:340)
    at clojure.lang.RT.loadResourceScript(RT.java:327)
    at clojure.lang.RT.loadResourceScript(RT.java:319)
    at clojure.main$load_script.invoke(main.clj:220)
    at clojure.main$script_opt.invoke(main.clj:273)
    at clojure.main$main.doInvoke(main.clj:354)
    at clojure.lang.RestFn.invoke(RestFn.java:409)
    at clojure.lang.Var.invoke(Var.java:365)
    at clojure.lang.AFn.applyToHelper(AFn.java:163)
    at clojure.lang.Var.applyTo(Var.java:482)
    at clojure.main.main(main.java:37)
Caused by: java.lang.IllegalArgumentException: No single method: f of interface: user.prot found for function: f of protocol: prot
    at clojure.lang.Compiler$InvokeExpr.<init>(Compiler.java:2880)
    at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3063)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5371)
    ... 24 more

为什么会这样?

1 个答案:

答案 0 :(得分:6)

据我所知,协议不支持可变参数。可能发生的是“&amp;”被视为参数符号而不是可变指标/列表理解。