Understanding Pointers in Go

In the world of programming, pointers serve a crucial role in managing memory and accessing data efficiently. Go, a popular language known for its concurrency and simplicity, employs pointers in a unique manner.

In the Go code example provided:

type Vertex struct {
    X, Y float64
}

func (v *Vertex) Abs() float64 {
    return math.Sqrt(v.X*v.X   v.Y*v.Y)
}

func main() {
    v := &Vertex{3, 4}
    fmt.Println(v.Abs())
}

we notice that the Abs method takes a pointer receiver (*Vertex), while the v variable is initialized with the address of the Vertex struct (&v). These two aspects reveal key behaviors of Go pointers.

The Magic of Method Derivation

Go allows us to derive a method with a pointer receiver from a method with a value receiver. This means that the func (v Vertex) Abs() float64 method in the example above will automatically generate an additional method implementation:

func (v Vertex) Abs() float64 { return math.Sqrt(v.X*v.X v.Y*v.Y) }
func (v *Vertex) Abs() float64 { return Vertex.Abs(*v) }  // GENERATED METHOD

When calling v.Abs() with the pointer v, the generated method will be automatically invoked. This derivation feature ensures that we can use both pointer and non-pointer receivers with the same method name.

Implicit Address Taking

Another intriguing aspect of Go pointers is the ability to automatically take the address of a variable. Consider the following code:

func (v *Vertex) Abs() float64 { return math.Sqrt(v.X*v.X v.Y*v.Y) }
func main() {
    v := Vertex{3, 4}
    v.Abs()
}

Here, the expression v.Abs() is equivalent to the following:

vp := &v
vp.Abs()

Go implicitly takes the address of the v variable, enabling us to directly call the Abs method without explicitly using the & operator. This implicit address taking simplifies code and enhances readability.

Memory Implications

While pointers can affect memory usage, it's important to note that in both scenarios, where we use *Vertex and Vertex as method receivers, the memory usage remains the same. Both implementations create a Vertex struct on the heap, and both access it through a pointer. There is no inherent memory benefit or penalty for using a pointer or non-pointer receiver in this particular example.