如何调用函数 which return 部分函数重载的函数

Question

如何使用以下 f 函数之一打印 "I'm not partial"，为什么下面的代码打印 "I'm partial"？也许有一些与函数相关的通用规则（可能与 arity 0）在 scala 中产生部分函数和名称重载？

object T1 extends App{    
  case class C()
  def f: PartialFunction[C, Unit] = { case c:C ⇒ println( "I'm partial") }
  def f(c: C): Unit = { println("I'm not partial") }
  (f:C ⇒ Unit)(C()) // Why this is printing "I'm partial"?
}

Answer 1

表达式不是应用程序。比较 x 的定义和模棱两可的调用：

scala> :pa
// Entering paste mode (ctrl-D to finish)

object T1 extends App{    
  case class C()
  def f: PartialFunction[C, Unit] = { case c:C ⇒ println( "I'm partial") }
  def f(c: C): Unit = { println("I'm not partial") }
  (f:C ⇒ Unit)(C()) // Why this is printing "I'm partial"?
}

// Exiting paste mode, now interpreting.

defined object T1

scala> T1 main null
I'm partial

scala> import T1._
import T1._

scala> val x: C => Unit = f
x: T1.C => Unit = <function1>

scala> f(C())
<console>:12: error: ambiguous reference to overloaded definition,
both method f in object T1 of type (c: T1.C)Unit
and  method f in object T1 of type => PartialFunction[T1.C,Unit]
match argument types (T1.C)
              f(C())
              ^

scala> x(C())
I'm partial

The spec 说 f 和 f(...)（第 3 条）一样具体，但不是相反（第 1 条）。

应用程序的括号意味着您正在比较两个看起来像 f(...).

的东西

如果这有帮助，通常的优先级排序方式：

scala> trait Helper { def f: PartialFunction[C, Unit] = { case c:C ⇒ println( "I'm partial") } }
defined trait Helper

scala> :pa
// Entering paste mode (ctrl-D to finish)

object T extends Helper {
def f(c: C): Unit = { println("I'm not partial") }
}

// Exiting paste mode, now interpreting.

defined object T

scala> T f new C
I'm not partial

还有其他 API 您可以编写但不能以正常方式调用：

scala> trait X { def f(i: => Int) = i }
defined trait X

scala> trait Y { def f(i: Int) = 2 * i }
defined trait Y

scala> class Z extends X with Y
defined class Z

scala> new Z().f(42)
res5: Int = 84

scala> typeOf[Z].members filter (_.name.toString == "f")
res7: Iterable[reflect.runtime.universe.Symbol] = SynchronizedOps(method f, method f)

scala> (new Z(): X).f(42)
res8: Int = 42

或者，无法在此处调用其他函数：

scala> class YY extends Y { def f(i: => Int) = i }
defined class YY

scala> new YY().f(42)
<console>:20: error: ambiguous reference to overloaded definition,
both method f in class YY of type (i: => Int)Int
and  method f in trait Y of type (i: Int)Int
match argument types (Int)
              new YY().f(42)
                       ^

scala> (new YY(): Y).f(42)
res15: Int = 84

如何调用函数 which return 部分函数重载的函数

How to call function overloaded by function which return partail function

scala

overloading

partialfunction