多次后期初始化 [英] Multiple late initialisation

问题描述

我找不到在scala中执行类似操作的自然方法:

I could not find a natural way to do something like that in scala :

class Car {
  var speed: Int
  var color: String
}

var myCar = new Car()

myCar.set {
  speed = 5
  color = "green"
}

我知道在Groovy等其他语言中也是可能的.我也知道我可以用这样的构造函数来做到这一点:

I know it is possible in other languages as Groovy. I also know I can do it with a constructor like this :

val myCar = new Car { 
  speed = 5
  color = "green"
}

我感兴趣的是这样做的一种方法，而不是在对象构造时，而是在对象创建完成之后，

I am interested in a way to do the same, not at the object construction but later, once the object has already been created

这是我到目前为止所做的:

This is what I have been doing so far :

class Car (var speed: Int, var color: String) {

  def set(f: (Car) => Unit) = {
    f(this)
  }

}

val myCar = new Car(5, "red")
myCar.set { c =>
  c.speed = 12
  c.color = "green"
}

但是我不喜欢为每个属性编写'c'变量

But I do not like the need to write the 'c' var for every attribute

关于如何操作或是否有更简单方法的任何想法??

Any idea on how I can do it or if there is an easier way ??

推荐答案

除非绝对必要，否则应避免使用可变的类.您通常会在Scala中执行此操作:

You should avoid mutable classes unless absolutely necessary. You would do normally this in Scala:

case class Car(speed: Int, color: String)

val c1 = Car(5, "red")
val c2 = c1.copy(speed = 12, color = "green")

(然后 c2 是汽车的新版本，而 c1 保持不变.)

(Then c2 is a new version of the car, while c1 remains unchanged.)

如果您想坚持使用可变类型，为什么不这么做

If you want to stick with your mutable type, why not just

class Car(var speed: Int, var color: String)

val myCar = new Car(5, "red")
import myCar._
speed = 12
color = "green"

---

使用专用的 set 方法:

class Car(var speed: Int, var color: String) {
  def set(speed: Int = this.speed, color: String = this.color): Unit = {
    this.speed = speed
    this.color = color
  }
}

val myCar = new Car(5, "red")
myCar.set(speed = 12, color = "green")
myCar.set(color = "blue")

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