Scala 类字段不可见 [英] Scala class fields not visible

问题描述

我有以下类，嵌套在名为 Solution 的对象中:

I have the following class, nested in an object called Solution:

class TreeNode(l_son: TreeNode, r_son: TreeNode,
               l_val: Int, r_val: Int, nr: Int)

此外，在对象 Solution 中，我尝试引用其字段:

Also, in the object Solution I try to reference its fields:

def query(left: Int, right: Int, node: TreeNode): Int = {
        var sum = 0;
        if(left <= node.l_val && node.r_val <= right) {
            sum = node.nr
        }

然而，每次我引用它的一个字段时，我都会收到一个错误:

However, every time I reference one of its fields, I get an error:

Solution.scala:36: 错误:值 l_val 不是 Solution.TreeNode 的成员if(left <= node.l_val && node.r_val <= right) {^Solution.scala:36: 错误:值 r_val 不是 Solution.TreeNode 的成员if(left <= node.l_val && node.r_val <= right) {^Solution.scala:37: 错误:值 nr 不是 Solution.TreeNode 的成员sum = node.nr

Solution.scala:36: error: value l_val is not a member of Solution.TreeNode if(left <= node.l_val && node.r_val <= right) { ^ Solution.scala:36: error: value r_val is not a member of Solution.TreeNode if(left <= node.l_val && node.r_val <= right) { ^ Solution.scala:37: error: value nr is not a member of Solution.TreeNode sum = node.nr

我认为 getter 和 setter 是为字段自动创建的.如果这是真的，为什么我不能访问它们?

I thought that getters and setters are created automatically for the fields. If that is true, why can't I access them?

推荐答案

像 class TreeNode(l_son: TreeNode, r_son: TreeNode,l_val: Int, r_val: Int, nr: Int)没有定义任何类成员，只是构造函数参数.你仍然可以在类体内使用它们，就像它们是成员一样(除了，你不能做 this.l_son)，因为整个体是在构造函数中定义的，所以它本质上是一个闭包.

A declaration like class TreeNode(l_son: TreeNode, r_son: TreeNode, l_val: Int, r_val: Int, nr: Int) does not define any class members, just constructor arguments. You can still use them inside the class body almost as if they were members (except, you can't do this.l_son), because entire body is defined inside the constructor, so it's essentially a closure.

要将类成员定义为构造函数参数，您必须在构造函数参数列表中以 val 或 var 为前缀:class TreeNode(val l_son: TreeNode ...)

To define a class member as a constructor parameter, you have to prefix it with val or var in the constructor parameter list: class TreeNode(val l_son: TreeNode ...)

Case 类的特殊之处在于它们会自动为每个构造函数参数创建一个(不可变的)成员，以及一堆其他使 case 类有用的自动成员.

Case classes are special in that they will create a (immutable) member for every constructor parameter automatically, along with a bunch of other automatic members that make case classes useful.

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