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34-embedding.go

@@ -1,22 +1,51 @@
 package main
 
 import "fmt"
+import "math"
 
-type Person struct {
-	Name string
+type Shape interface {
+    area() float64
 }
 
-func (p *Person) Talk() {
-    fmt.Println("Hi, my name is", p.Name)
+type Circle struct {
+    x, y, r float64
 }
 
-type Android struct {
-	Person
-	Model string
+func (c *Circle) area() float64 {
+    return math.Pi * c.r*c.r
+}
+
+type Rectangle struct {
+    x1, y1, x2, y2 float64
+}
+
+func distance(x1, y1, x2, y2 float64) float64 {
+    a := x2 - x1
+    b := y2 - y1
+    return math.Sqrt(a*a + b*b)
+}
+
+func (r *Rectangle) area() float64 {
+    l := distance(r.x1, r.y1, r.x1, r.y2)
+    w := distance(r.x1, r.y1, r.x2, r.y1)
+    return l * w
+}
+
+func totalArea(shapes ...Shape) float64 {
+    var area float64
+    for _, s := range shapes {
+        area += s.area()
+    }
+    return area
 }
 
 func main() {
-	android := new(Android)
-	android.Name = "Milo"
-	android.Talk()
+	circle := Circle{x: 0, y: 3, r: 5}
+	rectangle := Rectangle {x1: 3, x2: 10, y1: 5, y2: 7}
+
+	area := 0.0
+	for _, s := range []Shape{&circle, &rectangle} {
+		area += s.area()
+	}
+	fmt.Println(area)
 }

35-interfaces.go

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+type Shape interface {
+    area() float64
+}