Scala自我类型可以强制案例类类型吗 [英] can a scala self type enforce a case class type

问题描述

在scala中，有没有办法将特征的自身类型定义为案例类，例如任何案例类"?我希望自类型能够使用案例类的.copy方法，并强制其自身类型为 some 案例类，而不是常规类.我认为结构性类型无济于事，因为它们需要包含特定参数的签名(对于任何案例类，我可能一般都不能使用结构性类型).

Would there be any way in scala, to define a trait's self type to be a case class, as in "any case class"? I would like a self type to be able to use the .copy method of a case class, enforcing that its self type is some case class not a regular class. Structural types, I think, won't help, as they require a signature comprising specific arguments (I can probably not structural-type generically for any case class).

请放弃如果您需要做某些错误的事情"，因为我已经讲过，但是我的api设计-如果可以的话，将会变得很笨拙.我也很好奇下次.

Please forgo the "if you need that you must be doing something wrong", as I've already moved on but my api design - will have been slicker if the above were possible. I am also curious for next times around.

推荐答案

这仅适用于(根据您的建议)结构类型，并且仅适用于案例类参数类型的已知固定序列(您需要使用的确切签名) copy).例如:

This would only work using (as you suggest) structural types, and also only for a fixed known sequence of case class argument types (you need the exact signature of copy). For example:

trait InCase[Repr] {
  self: { def copy(foo: Int): Repr } =>

  def test(foo: Int): Repr = copy(foo)
}

case class Fail(foo: Int, bar: String) extends InCase[Fail] //illegal inheritance

case class Succeed(foo: Int) extends InCase[Succeed]

Succeed(123).test(456)

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