如何在 Scala 中转发重复的参数? [英] How do I forward repeated arguments in Scala?
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问题描述
在 Scala (2.7) 中,如果我有这个功能:
In Scala (2.7), if I have this function:
def foo(args: Array[String]) =
for (arg <- args) println(arg)
如果我现在尝试定义以下内容:
If I now try to define the following:
def bar(args: String*) = foo(args)
然后编译器抱怨:
<console>:5: error: type mismatch;
found : String*
required: Array[String]
def bar(args: String*) = foo(args)
^
我不明白这个错误,因为编程 Scala 书指出函数 bar
内的 args
的类型实际上是 Array[String]代码>.我应该如何编写这样一个带有重复参数的包装函数?
I don't understand this error, since the Programming Scala book states that the type of args
inside function bar
is actually Array[String]
. How am I supposed to write such a wrapper function with repeated arguments?
推荐答案
scala> def foo(args: Array[String]) = for(arg <- args) println(arg)
foo: (args: Array[String])Unit
scala> def bar(args: String*) = foo(args.toArray)
bar: (args: String*)Unit
scala> bar("hello", "world")
hello
world
您需要执行上述转换,因为 Scala 中的 varargs 实现为 Seq
,而不是 Array
.
You need to perform above conversion because varargs in Scala are implemented as Seq
, not Array
.
以下是在 Scala 中通常如何转发可变参数:
Here is how varargs are usually forwarded in Scala:
scala> def fooV(args: String*) = args foreach println
fooV: (args: String*)Unit
scala> def fooS(args: Seq[String]) = fooV(args: _*)
fooS: (args: Seq[String])Unit
scala> def bar(args: String*) = fooV(args: _*)
bar: (args: String*)Unit
scala> def barS(args: Seq[String]) = args foreach println
barS: (args: Seq[String])Unit
scala> def barV(args: String*) = barS(args)
barV: (args: String*)Unit
scala> def barV(args: String*) = barS(args.toSeq)
barV: (args: String*)Unit
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