What is the equivalent for LinkedList<T> in Golang - list

Question

In my use case, I would like to know how the following Java code would be implemented in Go
class TreeNode {
public int data;
public TreeNode left;
public TreeNode right;
public TreeNode(){}
}
LinkedList<TreeNode> treeList = new LinkedList<TreeNode>();
I am able to import the container/list package and add an interface. But it is not allowing any generic object. Do I have to implement my own version of list with TreeNode struct?
I just need to know how LinkedList<T> would work in Go.
EDIT 1: To make it clear, I am adding the complete code here. I am trying to find the linked list of all nodes at each depth in a binary tree. I used two packages list and binary tree. You can find the source code for binarytree here and list here. list is same as container/list but I added few extra functions
package main
import (
"fmt"
"go/chapter02-linkedlists/list"
"go/chapter04-treesandgraphs/binarytree"
)
func main() {
inArr := []int{4, 5, 7, 8, 9}
t1 := binarytree.NewMinimalHeightBST(inArr, 0, len(inArr)-1)
binarytree.InOrderTraverse(t1)
var nodeList []*list.List
nodeList = getLevelbasedList(t1, 0)
fmt.Println()
for _, value := range nodeList {
fmt.Print("[ ")
for x := value.Front(); x != nil; x = x.Next() {
fmt.Print(x.Value.(int), " ")
}
fmt.Println("]")
}
}
func getLevelbasedList(root *binarytree.Tree, level int) []*list.List {
if root == nil {
return nil
}
var nodeList []*list.List
parents := list.New()
current := list.New()
current.PushFront(root)
for current.Len() > 0 {
nodeList = append(nodeList, current)
parents = current
current = list.New()
for x := current.Front(); x != nil; x = x.Next() {
node := x.Value.(*binarytree.Tree)
if node.Left != nil {
current = current.PushFront(node.Left)
}
if node.Right != nil {
current = current.PushFront(node.Right)
}
}
return nodeList
}
}
And the error is,
./question4_4b.go:56: cannot use current.PushFront((interface {})(node.Left)) (type *list.Element) as type *list.List in assignment
./question4_4b.go:59: cannot use current.PushFront((interface {})(node.Right)) (type *list.Element) as type *list.List in assignment
EDIT 2: Based on JamesHenstridge's comment I edited from
current = current.PushFront(node.Left)
to
current.PushFront(node.Left)
And the issue resolved. But now I am getting interface conversion error,
[ panic: interface conversion: interface is *binarytree.Tree, not int
goroutine 1 [running]:

Answer 1

Go doesn't support generic types (see FAQ question Why does Go not have generic types?).
You have to use Type assertions to obtain the typed value you want.
E.g. create your TreeNode type:
type TreeNode struct {
Data int
Left *TreeNode
Right *TreeNode
}
And to iterate over a list containing TreeNode values:
l := list.New()
// Populate list
for e := l.Front(); e != nil; e = e.Next() {
if tn, ok := e.Value.(TreeNode); ok {
// do something with tn which is of type TreeNode
fmt.Println(tn)
} else {
// e.Value is not of type TreeNode
}
}
If you assemble the list and you can be sure it only contains values of type TreeNode, you can omit the error check in the type assertion and it becomes like this:
for e := l.Front(); e != nil; e = e.Next() {
// if e.Value would not be of type TreeNode, run-time panic would occur
tn := e.Value.(TreeNode) // tn is of type TreeNode
fmt.Println(tn)
}
Edit:
The error you're getting:
cannot use current.PushFront((interface {})(node.Left)) (type *list.Element)
as type *list.List in assignment
At line:
current = current.PushFront(node.Left)
The current variable is of type list.List, and the method current.PushFront() returns a value of type *list.Element. These are 2 different types, you can't assign a *Element to a variable that has a type of List.
Edit 2:
Your 2nd error:
panic: interface conversion: interface is *binarytree.Tree, not int
Is caused by the line:
fmt.Print(x.Value.(int), " ")
You try to assert that the value x.Value is of type int but it isn't! x.Value is of type *binarytree.Tree so the assertion will obviously fail.