由于*Wrong top statement declaration*
(我只能这样理解你的问题的一部分) - 你不能有构造函数对象object
是单身,所以你应该使用的情况下,类(ADT):
final case class TheDog(name: String) extends Animal
scala>TheDog("Spike")
res2_2: TheDog = TheDog("Spike")
val
和伴侣的对象与apply
为case类自动添加,所以你不需要在Animal
中定义你自己的apply
。 case class TheDog(val name: String)
与case class TheDog(name: String)
相同。
我也是用的,而不是抽象类trait
S:
trait Animal {
val name: String
def getSomething: String = {
"Dog: " + name
}
}
我不明白你的TypeClass
类型,但如果你真的想类型类:
trait Animal {
def name: String
}
final case class TheDog(name: String) extends Animal
final case class TheCat(name: String) extends Animal
implicit class RichDog(dog: TheDog){
def getSomething: String = {
"Dog" + dog.name
}
}
implicit class RichCat(cat: TheCat){
def getSomething: String = {
"Cat: " + cat.name
}
}
scala> TheDog("Spike").getSomething
res4_5: String = "DogSpike"
scala> TheCat("Tom").getSomething
res4_6: String = "Cat: Tom"
关于调用“隐含地”apply
,我不知道为什么有人需要这个,但是:
trait AnimalFactory[A <: Animal] {
def apply(name: String)(implicit constructor: String => A) = constructor(name)
}
object TheeeDog extends AnimalFactory[TheDog]
implicit def createDog(name: String) = TheDog(name)
TheeeDog("Spike")
当然,你必须提供createDog
并使其为客户可见的,但它并没有真正意义,如果你可以只使用抽象数据类型和定义附加要求apply
S IN同伴对象:
case class TheMouse(name: String)
object TheMouse{
def apply(isJerry: Boolean): TheMouse = if (isJerry) TheMouse("Jerry") else TheMouse("NotJerry")
}
TheMouse(true)
如果你想添加一些参数的构造函数,只需添加:
class AnimalFactory(clazz: SomeClass){
def doSomething = clazz.name
def apply(name: String)
}
val dogFactory = new AnimalFactory(dogClassDescriptor)
val catFactory = new AnimalFactory(catClassDescriptor)
dogFactory("Spike")
catFactory("Tom")
你甚至可以创建工厂工厂(我不建议 - 这SOLU重刑看起来已经过于复杂):
object AnimalFactory{ //please don't use classes for that - avoiding `new` is not their purpose
def apply(clazz: SomeClass) = new AnimalFactory(clazz)
}
val dogFactory = AnimalFactory(dogClassDescriptor)
//or even `val spike = AnimalFactory(dogClassDescriptor)("Spike")`
但还是有什么意义,如果你可以只提供基本clazz
无论是作为一个成员或只是一个包装:
final case class ClazzWrapper[T <: Animal](clazz: SomeClass, animal: T)
感谢深度解读。 –