clojure 中的匿名函数需要多少个参数? [英] How many arguments does an anonymous function expect in clojure?
问题描述
Clojure 如何确定匿名函数(使用 #...
符号创建)期望多少个参数?
How does Clojure determine how many arguments an anonymous function (created with the #...
notation) expect?
user=> (#(identity [2]) 14)
java.lang.IllegalArgumentException: Wrong number of args (1) passed to: user$eval3745$fn (NO_SOURCE_FILE:0)
推荐答案
#(println "Hello, world!")
-> no arguments
#(println "Hello, world!")
-> no arguments
#(println (str "Hello, " % "!"))
-> 1 个参数(%
是 %1
的同义词>)
#(println (str "Hello, " % "!"))
-> 1 argument (%
is a synonym for %1
)
#(println (str %1 ", " %2 "!"))
-> 2 个参数
等等.请注意,您不必使用所有 %n
s,预期的参数数量由最高的 n 定义.所以 #(println (str "Hello, " %2))
仍然需要两个参数.
and so on. Note that you do not have to use all %n
s, the number of arguments expected is defined by the highest n. So #(println (str "Hello, " %2))
still expects two arguments.
您也可以使用 %&
来捕获
You can also use %&
to capture rest args as in
(#(println "Hello" (apply str (interpose " and " %&))) "Jim" "John" "Jamey")
.
来自 Clojure 文档:
Anonymous function literal (#())
#(...) => (fn [args] (...))
where args are determined by the presence of argument literals taking the
form %, %n or %&. % is a synonym for %1, %n designates the nth arg (1-based),
and %& designates a rest arg. This is not a replacement for fn - idiomatic
used would be for very short one-off mapping/filter fns and the like.
#() forms cannot be nested.
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