scala - 多参数列表和默认参数

Question

编译此代码:

class Test {

  def f(arg: Int)(defaultArg: String => Unit = println): Unit = ???

  f(42)
}

失败
missing argument list for method f in class Test
[error] Unapplied methods are only converted to functions when a function type is expected.
[error] You can make this conversion explicit by writing `f _` or `f(_)(_)` instead of `f`.
[error] f(42)
[error] ^
[error] one error found

为什么会失败？它会引入歧义吗？是否可以使其工作而无需求助于单个参数列表？

Answer 1

您的情况的正确语法如下:

f(42)()

您可以通过将 defaultArg 定义为隐式来调用 f(42) 工作:

def f(arg: Int)(implicit defaultArg: String => Unit = println): Unit = ???

然后你可以调用它:

f(42)