在Scala的构造函数上重新分配var参数

Question

object ReassignTest extends App {
  class X(var i : Int)

  def x = new X(10)
  x.i = 20  // this line compiles

  println(x.i)  // this prints out 10 instead of 20, why?
}

那么我将如何为参数创建一个setter i

Answer 1

您定义x为一种方法,X每当您"调用"它时返回一个新方法.

def x = new X(10) //define a function 'x' which returns a new 'X'
x.i = 20  //create a new X and set i to 20

println(x.i) //create a new X and print the value of i (10)

定义x为一个值,而行为将如您所愿

val x = new X(10) //define a value 'x' which is equal to a new 'X'
x.i = 20  //set 'i' to be to 20 on the value 'x' defined above 

println(x.i) //print the current value of the variable i defined on the value 'x'