Scala选项？为什么有些人不继承AnyVal,为什么它不是值类型？

发布时间：2020-12-16 19:17:17 所属栏目：安全来源：网络整理

导读：为什么 Scala有些不从AnyVal继承,以便它使用值类型功能并保存拳击成本？就像是： sealed trait TestOption[+A] extends Any { def isEmpty: Boolean def get: A}final case class TestSome[+A](val x: A) extends AnyVal with TestOption[A] { def isEmpty

为什么 Scala有些不从AnyVal继承,以便它使用值类型功能并保存拳击成本？

就像是：

sealed trait TestOption[+A] extends Any {
  def isEmpty: Boolean
  def get: A
}

final case class TestSome[+A](val x: A) extends AnyVal with TestOption[A] {
  def isEmpty = false
  def get = x
} 

case object TestNone extends TestOption[Nothing] {
  def isEmpty = true
  def get = throw new NoSuchElementException("None.get")
}

解决方法

从 Value Classes的文档：

Summary of Limitations

A value class

must have only a primary constructor with exactly one public,val parameter whose type is not a value class. (From Scala 2.11.0,the
parameter may be non-public.)

may not have specialized type parameters.

may not have nested or local classes,traits,or objects

may not define a equals or hashCode method.

must be a top-level class or a member of a statically accessible object

can only have defs as members. In particular,it cannot have lazy vals,vars,or vals as members.

cannot be extended by another class.

大胆的将一些人排除在当前写成的价值等级之外.其中的第二个可能会通过稍微改变来解决,但前者会将其杀死.如果某些值本身成为值类,则无法在其中包含另一个值类.

（编辑：李大同）

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