由于使用私有 [this] 而不是私有，行为上的意外差异似乎 [英] Unexpected difference in behavior seemingly due to using private[this] instead of private

问题描述

这两个类的行为不同；原因似乎与使用 private[this] 声明而不是 private 相关.有人能解释一下原因吗?

These two classes behave differently; the cause seems related to the use of a private[this] declaration instead of a private. Can somebody explain why, please?

• 私有:

class Person(
  private var _age: Int
) {
  if (_age < 0) { _age = 0 }

  def age = _age
  def age_=(newAge: Int) {
    if (newAge > _age) { _age = newAge }
  }
}

在 REPL 中，这与我对两个类所期望的一样；即age方法得到_age，在构造时已经设置为合适的值:

In the REPL, this behaves as I was expecting for both classes; that is, the age method gets _age, which has been set to the appropriate value during construction:

scala> val person = new Person(-1)
person: Person = Person@200a570f

scala> person.age
res0: Int = 0

private[this]:

class Person(
  private[this] var _age: Int
) {
  if (_age < 0) { _age = 0 }

  def age = _age
  def age_=(newAge: Int) {
    if (newAge > _age) { _age = newAge }
  }
}

在 REPL 中，person.age 似乎在对 if 表达式求值之前取 _age 的值.不过，在使用 setter 后，它按预期工作:

In the REPL, person.age appears to take the value of _age prior to the evaluation of the if expression. It works as expected after using the setter, though:

scala> val person = new Person(-1)
person: Person = Person@6f75e721

scala> person.age
res0: Int = -1

scala> person.age = 0
person.age: Int = 0

scala> person.age
res1: Int = 0

推荐答案

这是一个已知的错误，即 SI-6880.

This is a known bug, namely SI-6880.

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