Golang pointer confusion, how to get the pointer from the function and then pass it to the modifying function

Question content

I want to use a library (golang walk declarative) which wants me to pass a pointer variable and the library will use an instance later Fill it.

For bookkeeping purposes I tried creating a function to return the reference and passing it further, but in the original function I did not get back the reference to the correct object.

I tried to simplify the problem but I still can't figure it out correctly, how to populate the value world into a map inside the test_ref structure without modifying the setup function.

Working code

<code>var t *walk.LineEdit
...
                    LineEdit{
                        AssignTo: &t,
                    },
</code>

My attempt

LineEdit{
                        AssignTo: GetLineEdit("msg"),
                    },
...
func GetLineEdit(name string) **walk.LineEdit {

Test code

type test_ref struct {
    v map[string]*string
}

func (t *test_ref) init() {
    t.v = map[string]*string{}
}

func (t *test_ref) return_ref() **string {
    s := "hello"
    t.v["a"] = &s
    p := t.v["a"]
    return &p
}

type test_setup struct {
    s **string
}

//dont modify this function
func setup(t test_setup) {
    w := "world"
    *(t.s) = &w
}

func main() {
    tr := test_ref{}
    tr.init()
    s := tr.return_ref()
    setup(test_setup{
        s: s,
    })
    fmt.Println(*tr.v["a"])//logging hello

}

If I make a small modification to the setup function, I can get it to work, but since I don't want to update the walking library, I was wondering if there is a way to do this without touching the setup function.

<code>func setup(t test_setup) {
    w := "world"
    **(t.s) = w
}
</code>

Correct answer

Here:

func (t *test_ref) return_ref() **string {
    s := "hello"
    t.v["a"] = &s
    p := t.v["a"]
    return &p
}

What you returned is the address of variable p.

I think this is what you are trying to do:

func (t *test_ref) return_ref() *string {
    s := "hello"
    t.v["a"] = &s
    return &s
}

The above will return the address of s, which is what is stored in the map. Then:

Chapter 823

This will set the value of the string to "world".

You can further your education and do the following:

type test_ref struct {
    v map[string]**string
}

func (t *test_ref) init() {
    t.v = map[string]**string{}
}

func (t *test_ref) return_ref() **string {
    s := "hello"
    k := &s
    t.v["a"] = &k
    return &k
}

type test_setup struct {
    s **string
}

// dont modify this function
func setup(t test_setup) {
    w := "world"
    *(t.s) = &w
}

func main() {
    tr := test_ref{}
    tr.init()
    s := tr.return_ref()
    setup(test_setup{
        s: s,
    })
    fmt.Println(**tr.v["a"]) //logging hello

}

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