为什么 Scala 在按名称参数重载的情况下的行为与按值参数的情况不同? [英] Why is Scala's behavior in case of overloading with by-name parameters different from the case with by-value parameters?

问题描述

鉴于此 Scala 代码:

Given this Scala code:

object test {

  def byval(a: Int) = println("Int")
  def byval(a: Long) = println("Long")

  def byname(a: => Int) = println("=> Int")
  def byname(a: => Long) = println("=> Long")

  def main(args: Array[String]) {
      byval(5)
      byname(5)
  }
}

调用 byval(5) 编译正确，但 byname 编译失败:

the call byval(5) compiles correctly, but byname fails to compile:

ambiguous reference to overloaded definition

为什么?我希望在重载方面观察到按值和按名称参数的相同行为……如何修复?

Why? I would expect to observe the same behavior for by-value and by-name parameters with respect to overloading… How can it be fixed?

推荐答案

那是因为 JVM 不支持by-name"参数，所以 Scala 必须以另一种方式实现它.<代码>=>X 实际上编译成一个 Function0[X]，它擦除为 Function0[Object]，这使得 Scala 无法区分两个仅通过按名称参数的预期类型.

That's because JVM does not support a "by-name" parameter, so Scala has to implement it in another way. => X actually compiles to a Function0[X], which erases to Function0[Object], which makes it impossible for Scala to distinguish two methods that differ only by the expected type of a by-name parameter.

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