The Go Programming Language

6.1 Method Declarations

A method is declared with a variant of the ordinary function declaration in which an extra parameter appears before the function name. The parameter attaches the function to the type of that parameter.

Let’s write our first method in a simple package for plane geometry:

Click here to view code image

gopl.io/ch6/geometry

package geometry

import "math"

type Point struct{ X, Y float64 }

// traditional function
func Distance(p, q Point) float64 {
    return math.Hypot(q.X-p.X, q.Y-p.Y)
}

// same thing, but as a method of the Point type
func (p Point) Distance(q Point) float64 {
    return math.Hypot(q.X-p.X, q.Y-p.Y)
}

The extra parameter p is called the method’s receiver, a legacy from early object-oriented languages that ...