Scala 添加方法来扩展某些东西
我在 BinarySearchTree 中创建了 lowerBound 方法。
BinarySearchTree 扩展了 TreeMap[Int, Int]。
所以我在BinarySearchTree中做了lowerBound方法。
但编译器说
treetest.scala:85: error: value lowerNeighbor is not a member of TreeMap[Int,Int] t2.lowerNeighbor(3)
How to made it? :)
class BinarySearchTree(private val root: Node) extends TreeMap[Int, Int] {
def lowerNeighbor(x : Int) : Int = {
var t = root
.........
}
}
var t2: TreeMap[Int, Int] = new BinarySearchTree
t2.lowerNeighbor(3)
I made lowerBound method in my BinarySearchTree.
BinarySearchTree extends TreeMap[Int, Int].
So I made lowerBound method in BinarySearchTree.
but compiler said
treetest.scala:85: error: value lowerNeighbor is not a member of TreeMap[Int,Int] t2.lowerNeighbor(3)
How to made it? :)
class BinarySearchTree(private val root: Node) extends TreeMap[Int, Int] {
def lowerNeighbor(x : Int) : Int = {
var t = root
.........
}
}
var t2: TreeMap[Int, Int] = new BinarySearchTree
t2.lowerNeighbor(3)
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您已将
t2变量声明为静态类型TreeMap[Int, Int]。因此，对于编译器来说，每次使用t2时，它都会假设它是TreeMap[Int, Int]的实例。lowerNeighbor不是在TreeMap上定义的方法，而是在BinarySearchTree上定义的方法。如果您想调用lowerNeighbor方法，变量的静态类型必须是BinarySearchTree。** 这会忽略隐式转换，您可能需要阅读一旦您弄清楚静态类型与动态类型问题，就可以继续。
You have declared your
t2variable to be of the static typeTreeMap[Int, Int]. Therefore, for the compiler, each time you uset2, it will assume it is an instance ofTreeMap[Int, Int].lowerNeighboris not a method defined onTreeMaps, but onBinarySearchTrees. The static type of your variable has to beBinarySearchTreeif you want to call thelowerNeighbormethod.** This is ignoring implicit conversions, which you may want to read up on once you've figured out the static type vs. dynamic type issue.