update book code

eBook/exercises/chapter_11/point_interfaces.go

@@ -0,0 +1,89 @@
+// float64 is necessary as input to math.Sqrt()
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+type Magnitude interface {
+	Abs() float64 
+}
+
+var m Magnitude
+
+type Point struct {
+	X, Y float64 
+}
+
+func (p *Point) Scale(s float64) {
+	p.X *= s
+	p.Y *= s 
+}
+
+func (p *Point) Abs() float64 {
+	return math.Sqrt(float64(p.X*p.X + p.Y*p.Y))
+}
+
+type Point3 struct {
+	X, Y, Z float64
+}
+
+func (p *Point3) Abs() float64 {
+	return math.Sqrt(float64(p.X*p.X + p.Y*p.Y + p.Z*p.Z))
+}
+
+type Polar struct {
+	R, Theta float64
+}
+
+func (p Polar) Abs() float64 { return p.R }
+
+func main() {
+	p1 := new(Point)
+	p1.X = 3
+	p1.Y = 4
+	m = p1 // p1 is type *Point, has method Abs()
+	fmt.Printf("The length of the vector p1 is: %f\n", m.Abs())
+
+	p2:= &Point{4, 5}
+	m = p2
+	fmt.Printf("The length of the vector p2 is: %f\n", m.Abs() )
+	
+	p1.Scale(5)
+	m = p1
+	fmt.Printf("The length of the vector p1 after scaling is: %f\n", m.Abs() )
+	fmt.Printf("Point p1 after scaling has the following coordinates: X %f - Y %f\n", p1.X, p1.Y)
+	
+	mag := m.Abs()
+	m = &Point3{3, 4, 5}
+	mag += m.Abs()
+	m = Polar{2.0, math.Pi / 2}
+	mag += m.Abs()
+	fmt.Printf("The float64 mag is now: %f", mag )
+}
+/* Output:
+The length of the vector p1 is: 5.000000
+The length of the vector p2 is: 6.403124
+The length of the vector p1 after scaling is: 25.000000
+Point p1 after scaling has the following coordinates: X 15.000000 - Y 20.000000
+The float64 mag is now: 34.071068
+
+-- instead of:
+func (p *Point) Abs() float64 {
+	return math.Sqrt(float64(p.X*p.X + p.Y*p.Y))
+}
+m = p1
+we can write:
+func (p Point) Abs() float64 {
+	return math.Sqrt(float64(p.X*p.X + p.Y*p.Y))
+}
+m = p1
+and instead of:
+func (p Polar) Abs() float64 { return p.R }
+m = Polar{2.0, math.Pi / 2}
+we can write:
+func (p *Polar) Abs() float64 { return p.R }
+m = &Polar{2.0, math.Pi / 2}
+with the same output
+*/