更新不可变对象 [英] Updating immutable objects

问题描述

  class Player（val name：String，val onField：Boolean，val draft： Int，val perc：Int，val height：Int，val timePlayed：Int）{
 override def toString：String = name 
  

}

我想要做的是

  def play（team：List [Player]）：List [Player] = 
 team map（p => new Player（p.name，p.onField，p.draft，p.perc， p.height，p.timePlayed + 1））
  

这实际上增加了字段timePlayed一个，并返回新的列表的球员。

有没有更方便的方法来做到这一点？也许：

  def play（team：List [Player]）：List [Player] = 
 team map（p => p.timeIncremented（））
  

我的问题是如何在更多方便的方法？所以我不必这样做：

 新玩家（p.name，p.onField，p.draft，p .perc，p.height，p.timePlayed + 1）
  

谢谢！

解决方案

您可以使用define Player作为 case class 并使用编译器生成的方法 copy ：

  case class Player（name：String，onField：Boolean，draft：Int， perc：Int，height：Int，timePlayed：Int）{
 override def toString：String = name 
} 
 
 def play（team：List [Player]）：List [ Player] = 
 team map（p => p.copy（timePlayed = p.timePlayed + 1））
  

另外，正如你所看到的，默认情况下，构造函数的参数是 val 。

在播放器中定义 timeIncremented ，并按照您的要求使用它：

  case class Player（name：String，onField：Boolean，draft：Int，perc：Int，height：Int，timePlayed：Int）{ 
覆盖def toString：String = name 
 def timeIncremented：Player = copy（timePlayed = this.timePlayed + 1）
} 
 
 def play（team：List [ Player]）：List [Player] = 
 team map（_.timeIncremented）
  

更复杂的情况下，你可以看看镜头：

http://akisaarinen.fi/blog/2012/12/07/boilerplate-free-functional-lenses-for-scala/

更新嵌套结构的方法

I have the following class built:

class Player(val name: String, val onField: Boolean, val draft: Int, val perc: Int, val height: Int, val timePlayed: Int) {
override def toString: String = name

}

I'm trying to do

def play(team: List[Player]): List[Player] =
team map (p => new Player(p.name, p.onField, p.draft, p.perc, p.height, p.timePlayed + 1))

which is actually incrementing the field "timePlayed" by one, and return the new "List" of players.

Is there a more convenient way to do this? Perhaps:

def play(team: List[Player]): List[Player] =
team map (p => p.timeIncremented())

My question is how to implement timeIncremented() in a more convenient way? so that I don't have to do:

new Player(p.name, p.onField, p.draft, p.perc, p.height, p.timePlayed + 1)

Thanks!

解决方案

You can use define Player as case class and use compiler generated method copy:

case class Player(name: String, onField: Boolean, draft: Int, perc: Int, height: Int, timePlayed: Int) {
    override def toString: String = name
}

def play(team: List[Player]): List[Player] =
    team map (p => p.copy(timePlayed = p.timePlayed + 1))

Also, as you see, constructor parameters are val by default.

And you can define timeIncremented in Player and use it exactly as you want:

case class Player(name: String, onField: Boolean, draft: Int, perc: Int, height: Int, timePlayed: Int) {
    override def toString: String = name
    def timeIncremented: Player = copy(timePlayed = this.timePlayed + 1)
}

def play(team: List[Player]): List[Player] =
    team map (_.timeIncremented)

For more complex cases you can take a look at lenses:
http://akisaarinen.fi/blog/2012/12/07/boilerplate-free-functional-lenses-for-scala/
Cleaner way to update nested structures

这篇关于更新不可变对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！