问题描述
我想为未指定数量的函数参数创建一些函数
I want to make some function for unspecified number of arguments of function
例如
scala> def test(fx: (String*) => Boolean, arg: String*): Boolean = fx(arg: _*)
test: (fx: String* => Boolean, arg: String*)Boolean
scala> def AA(arg1: String, arg2: String) :Boolean = {
println ("Arg1 : " + arg1 + " Arg2 : " + arg2)
true}
AA: (arg1: String, arg2: String)Boolean
scala> test(AA,"ASDF","BBBB")
<console>:10: error: type mismatch;
found : (String, String) => Boolean
required: String* => Boolean
test(AA,"ASDF","BBBB")
^
我该如何解决这个问题??
How can I solve this problem??
推荐答案
这可以通过使用 shapeless 和 ProductArgs 以及类似于我的 回答另一个问题.
This could be done using shapeless with ProductArgs and something similar to my answer to another question.
import shapeless.{HList, ProductArgs}
import shapeless.ops.hlist.IsHCons
import shapeless.ops.function.FnToProduct
import shapeless.syntax.std.function._
object test extends ProductArgs {
def applyProduct[L <: HList, NarrowArgs <: HList, Args <: HList, F, R](
l: L
)(implicit
ihc: IsHCons.Aux[L, F, NarrowArgs],
ftp: FnToProduct.Aux[F, Args => R],
ev: NarrowArgs <:< Args
): R = {
val (func, args) = (l.head, l.tail)
func.toProduct(args)
}
}
您可以用作:
def aa(s1: String) = s1.length
def bb(s1: String, s2: String) = s1 * s2.length
test(aa _, "foo") // Int = 3
test(bb _, "foo", "bar") // String = foofoofoo
// test(aa _, "foo", "bar") doesn't compile
扩展 ProductArgs 转换或 test(aa _, "foo")(实际上是 test.apply(aa _, "foo")code>) 到 test.applyProduct((aa _) :: "foo" :: HNil).在 applyProduct 中，我们检查 HList 是否包含一个函数和有效参数.
Extending ProductArgs transforms or test(aa _, "foo") (which is actually test.apply(aa _, "foo")) to test.applyProduct((aa _) :: "foo" :: HNil). In applyProduct we check that the HList consists of a function and valid arguments.
我们不需要 NarrowArgs <:<参数，但ProductArgs 似乎给出与 SingletonProductArgs.
这篇关于如何在 Scala 中为未指定数量的参数函数创建函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！