Methods

Here, we declare the isAdult method on the *Person type.

func (p *Person) isAdult bool {
  return p.Age > 18
}

In Go, Methods are functions that have a special receiver argument:

// The Abs() method a receiver argument of type Vertex named v.
func (v Vertex) Abs() float64 {
	return math.Sqrt(v.X*v.X + v.Y*v.Y)
}

The receiver argument can be either a value receiver or a pointer receiver

• value receiver - makes a copy of the type and passes it to the function so that it has its own local version.
  • Therefore, the original object will remain unchanged.
  • ex. (v Vertex)
• pointer receiver - passes the address of a type to the function. The function stack has a reference to the original object.
  • Therefore, any modifications on the passed object will modify the original object.
  • ex. (v *Vertex)

Since methods often need to modify their receiver, pointer receivers (ie. *x) are more common than value receivers.

Pointer Receiver

In this case the receiver argument is a pointer, as denoted by *T:

func (v *Vertex) Scale(f float64) {
	v.X = v.X * f
	v.Y = v.Y * f
}

• in this case, the Scale method has as a receiver argument *Vertex.
• now, we can modify the value to which the receiver points

methods with pointer receivers take either a value or a pointer as the receiver when they are called

• this means that you can pass either the value or the pointer to the value (ie. either v or &v)
• this is a convenience offered by the Go engine. Under the hood, Go interprets the statement v.Scale(5) as (&v).Scale(5) since the Scale method has a pointer receiver.

func (v *Vertex) Scale(f float64) {
	v.X = v.X * f
	v.Y = v.Y * f
}

In general, all methods on a given type should have either value or pointer receivers, but not a mixture of both.