Question

如何使用以下f函数之一打印“我不偏袒”，为什么下面的代码会打印“我偏爱”？也许有一些与函数相关的通用规则（可能是arity 0）在scala中产生了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。将x的定义与模糊调用进行比较：

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表示f与f(...)（第3章）具体相同，但不相反（通过项目符号1）。

应用程序的parens意味着您要比较两个看起来像f(...)的东西。

如果这有帮助，通常的优先顺序排列方式：

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

您可以编写其他API，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

如何通过返回部分函数的函数调用函数重载

1 个答案: