Scala中辅助构造函数的用例是什么？

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例如，这是怎么回事：

class Cat(name: String, val age: Int) {
  def this() = this("Garfield", 20)
}

val someCat = new Cat
someCat.age
res0: Int = 20

不同于：

class Cat(name: String = "Garfield", val age: Int = 20)
val someCat = new Cat
someCat.age
res0: Int = 20

Note: I have seen answers to other questions(e.g here) that discuss the differences between Java & Scala in the implementation for auxiliary constructors. But I am mostly trying to understand why do we need them in Scala, in the first place.

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  • (艮)悲伤
    (艮)悲伤 回复

    辅助构造函数不仅可以提供默认值，还可以带来更多好处。例如，以下示例可以接受不同类型的参数：

    class MyBigInt(x: Int) {
  def this(s: String) = this(s.toInt)
}

    如果主构造函数包含实现详细信息，您还可以隐藏它：

    class MyBigInt private(private val data: List[Byte]) {
  def this(s: String) = this(...)
  def this(n: Int) = this(...)
}

    This allows you to have data clearly be the backing structure for your class while avoiding cluttering your class with the arguments to one of your auxiliary constructors.

    辅助构造函数的另一个用途是将Java代码迁移到Scala，而不会破坏依赖关系。