How can I get the real pointer to a field inside a struct in Go?

Question

I have a struct, say:

type sample struct{
   data []float64
}

Now, I declare a method:

func (s sample) Get() *[]float64{
return &s.data
}

I am trying to append to this slice via the pointer I got via Get()

func main(){
example := sample{[]float64{1,2,3}}

//Here I will append:
pointerToArray := example.Get()
*pointerToArray = append(*pointerToArray, 4)
fmt.Println(example.Get()) // still shows only &{1,2,3}
}

I have a general idea of why this is happening: The function Get is returning the address of its local scope, and I have fixed it by change the struct itself to

type sample struct{
data *[]float64
}

for which the code returns the expected &{1,2,3,4}

Now, for my question: Is there anyway to get the real pointer to the field in the struct through a getter method without using a pointer field directly in the struct?

Answer 1

The problem is that you've defined the Get method with a struct receiver, rather than on a pointer. That means when you return &s.data you get the address of the field of receiver, rather than from the original struct. You can fix this simply by using a pointer receiver:

func (s *sample) Get() *[]float64{
    return &s.data
}

Here's a complete runnable example ( https://play.golang.org/p/AIj8QOYfx85 )

package main

import "fmt"

type sample struct {
    data []float64
}

func (s *sample) Get() *[]float64 {
    return &s.data
}

func main() {
    example := sample{[]float64{1, 2, 3}}

    p := example.Get()
    *p = append(*p, 4)
    fmt.Println(example.Get())
}