我想使用一些
case classval base: Base = new Derived
println(base.copy())
我不能将
BaseDerivedCannot resolve symbol copyabstract class BaseWorkaround(name: String) {
def dispatchCopy: BaseWorkaround
}
case class DerivedWorkaround(name: String) extends BaseWorkaround(name) {
override def dispatchCopy: BaseWorkaround = copy()
}
val abbie: BaseWorkaround = DerivedWorkaround("Abbie")
println(abbie.dispatchCopy)
解决方法有效，但看起来很麻烦。有没有更优雅的方式来执行此行为？
从根本上说，您不能继承
copycopy你正在做的工作，但是，如果你仔细想想，它是相当无用的：案例类是（或者，应该是设计的）不可变的，所以，如果
foofoo foo.copy()foocloneBaseCloneablecopyDerived.copydef copy(name: String = name)val foo = Derived("foo"); val bar = foo.copy("bar")所以，如果你知道你的案例类将有哪些参数，你可以这样做：
abstract class Base[T <: Base] {
def name: String;
def copy(name: String = name): T
}
case class Derived1(name: String) extends Base[Derived1]
case class Derived2(name: String) extends Base[Derived2]
val p: Base[_] = Derived1("foo")
val pCopy = p.copy()
val s: Base[_] = Derived2("bar")
val sCopy = s.copy
请注意，虽然
Derived1Derived2Base 中定义的参数集不同的参数集定义子类// This won't compile:
class Derived3(name: String, code: Int) extends Base[Derived3]
您可以刷新为什么案例类的继承不好以及可能的解决方法的信息：
案例类适用于函数式编程中的代数数据类型：
sealed trait Base
case class Derived1(i: Int) extends Base
case class Derived2(s: String) extends Base
OOP 和他们的继承很奇怪。 你应该更喜欢组合而不是继承：
case class Base(s: String)
case class Derived(i: Int, b: Base)
案例类还有其他选择：
http://eed3si9n.com/contraband-an-alternative-to-case-class/
https://www.scala-sbt.org/contraband/
https://www.scala-sbt.org/1.x/docs/Datatype.html（sbt-datatype）
https://github.com/sbt/contraband
https://www.reddit.com/r/scala/comments/5xu085/contraband_an_alternative_to_case_class/
@datahttps://gitlab.com/fommil/attic/tree/master/石笋
@datahttps://github.com/alexarchambault/data-class
@data@root@branch@leaf@root@branch@astapply/unapplycopyhttps://svejcar.dev/posts/2019/09/26/better-tostring-alternative-for-case-classes/
让我们想想
copyBasesealed trait Base {
type This <: Base
def name: String
def age: Int
def copy(name: String = name, age: Int = age): This
}
case class Derived(name: String, age: Int) extends Base {
type This = Derived
def copy(name: String = name, age: Int = age): Derived = Derived(name, age)
}
或
sealed trait Base {
def name: String
def age: Int
def copy(name: String = name, age: Int = age): Base
}
case class Derived(name: String, age: Int) extends Base {
def copy(name: String = name, age: Int = age): Derived = Derived(name, age)
}
原则上，
def copyDeriveddef copyBasedef namedef agecase class Derived(name: String, age: Int)BaseBaseDerived