Go Interfaces

func main() { var r Shape = Rectangle{Length: 3, Width: 4} fmt.Printf("Type of r: %T, Area: %v, Perimeter: %v.", r, r.Area(), r.Perimeter()) } 

func (r Rectangle) Area() float64 { return r.Length * r.Width } func (r Rectangle) Perimeter() float64 { return 2 * (r.Length + r.Width) } 

The methods defined in Shape are implemented in Rectangle.

type Rectangle struct { Length, Width float64 } 

Struct Rectangle implicitly implements interface Shape by implementing all of its methods.

type Shape interface { Area() float64 Perimeter() float64 }