How 'pass by value slice' and 'the underlying array' behaves in Golang?

I am trying to implement a depth first search in GO and I am facing below issue.

In GO whenever we pass a slice to a function it should create a new slice header as GO is pass by value language but at the same time newly created slice should point to the same underlying array to which previous slice was pointing.

But Looks like in my depth first search function, passed slice is not pointing to the same array.

As we can see in below mentioned code I am calling depth first traverse function recursively with node and slice as parameters where slice stores the value for each visited node. After traversing entire tree I should get all the nodes in the slice but the slice was empty.

func (b *BinarySearchTree) DFSInOrder(node *Node, list []int) {

	if node.Left != nil {
		b.DFSInOrder(node.Left, list)
	}

	list = append(list, node.Value)

	if node.Right != nil {
		b.DFSInOrder(node.Right, list)
	}
}

func main() {
    //...
	//BinarySearchTree creation code
    //...
	
	var list []int
	b.DFSInOrder(b.Root, list)
	fmt.Println()
	fmt.Println("List after traversing:", list)
}

Ideally in each recursive call even if it is creating new slice it should update the same underlying array and finally original slice should have all the nodes but it was empty.

Can some one please explain why this is happening?

Please find full code for more details here: https://play.golang.com/p/PCrADg3zYV8 <br>
Check function at line 51.

Note: If I pass slice pointer(list *[]int) then it works fine.

See this example go playground. append is allocating a new slice, and saving the new slice to the value, not the reference. You are correct, you don't need to pass a slice by reference to modify the underlying elements which is what the editSlice function does in my example.

package main

import (
	"fmt"
)

func main() {
	slice := []int{10, 20}
	appendSlice(slice)
	fmt.Println("slice after append ", slice)

	editSlice(slice)
	fmt.Println("slice after edit ", slice)
}

func appendSlice(s []int) {
	s = append(s, s[0])
	fmt.Println("the appended slice ", s)
}

func editSlice(s []int) {
	s[0] = s[0] * 2
}

If you still want to use the append syntax in your code, I updated it to pass and modify the slice by reference (go playground).