Golang Pointers as method param

Question

I am working with golang's pointers the way I did with c++, but it seems not to work, which would be the right way to do it? or what am I doing wrong?, Thanks.

ftw I'm doing AsyncBinaryTrees.

type Obj interface {
    Compare(node Obj) int
}

type Tree struct {
    Item        Obj
    Rigth, Left *Tree
    height      int16
}

func Insert(t *Tree, item Obj) chan struct{} {
    done := make(chan struct{}, 1)
    go insert(t, item, done)
    return done
}

func insert(t *Tree, item Obj, done chan struct{}) {
    if t == nil {
        t = &Tree{Item: nil, Rigth: nil, Left: nil, height: 0}
        var signal struct{}
        done <- signal
        close(done)
    } else {
        if t.Item.Compare(item) == 1 { //Left
            insert(t.Left, item, done)
        } else if t.Item.Compare(item) == -1 { //Rigth
            insert(t.Right, item, done)
        } else {
            close(done)
            panic
        }
    }
}

//=== testing

func assertSignal(ch_signal chan struct{}, t *testing.T) {
    _, done := <-ch_signal
    if !done {
        t.Error("Error: it should send a signal of empty struct")
    }
}

func TestInsertion(t *testing.T) {
    var tree *Tree
    ch_signal := Insert(tree, newObjInt())
    fmt.PrintLn(t)             //=> <nil>
    assertSignal(ch_signal, t) //=>PASS
    ch_signal = Insert(tree, newObjInt())
    fmt.PrintLn(t)             //=> <nil>
    assertSignal(ch_signal, t) //=>PASS
    ch_signal = Insert(tree, newObjInt())
    fmt.PrintLn(t)             //=> <nil>
    assertSignal(ch_signal, t) //=>PASS
    ch_signal = Insert(tree, newObjInt())
    assertSignal(ch_signal, t) //=>PASS
}

nil

nil

nil

TEST PASS

Answer 1

In your insert function you have:

func insert(t *Tree, item Obj, done chan struct{}) {
    if t == nil {
        t = &Tree{Item: nil, Rigth: nil, Left: nil, height: 0}
    ...
}

This updates the local variable t , but will not change the variable passed in the calling scope since Go passes function parameters by value. So when you make the following call:

insert(t.Left, item, done)

if t.Left is nil , its value will not be changed by the function call. If you do want it to update the variable, you'll need to define the function argument as t **Tree , change references to set *t instead, and change the call to:

insert(&t.Left, item, done)

There is no equivalent to C++'s syntax for passing function arguments by reference: instead you need to be explicit when passing pointers.