Defining golang struct function using pointer or not

Question

Can someone explain to me why appending to an array works when you do this:

func (s *Sample) Append(name string) {
    d := &Stuff{
        name: name,
    }         


        

Answer 1

Go slices are a tricky beast. Internally, a variable of slice type (like []int) looks like this:

struct {
    data *int // pointer to the data area
    len  int
    cap  int
}

When you pass a slice to a function, this structure is passed by value, while the underlying data area (i.e. what data points to) is not copied. The builtin append() function modifies the data area (or generates a new one) and returns a new slice with updated len, data, and cap values. If you want to overwrite anything that is not part of the underlying data area, you need to pass a pointer to the slice or return a modified slice.