update book code

eBook/exercises/chapter_14/gofibonacci3.go

@@ -0,0 +1,45 @@
+// courtesy of: http://sdh33b.blogspot.com/2009/12/fibonacci-in-go.html
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func dup3(in <-chan int) (<-chan int, <-chan int, <-chan int) {
+	a, b, c := make(chan int, 2), make(chan int, 2), make(chan int, 2)
+	go func() {
+		for {
+			x := <-in
+			a <- x
+			b <- x
+			c <- x
+		}
+	}()
+	return a, b, c
+}
+
+func fib() <-chan int {
+	x := make(chan int, 2)
+	a, b, out := dup3(x)
+	go func() {
+		x <- 0
+		x <- 1
+		<-a
+		for {
+			x <- <-a + <-b
+		}
+	}()
+	return out
+}
+
+func main() {
+	start := time.Now()
+	x := fib()
+	for i := 0; i < 10; i++ {
+		fmt.Println(<-x)
+	}
+	end := time.Now()
+	delta := end.Sub(start)
+	fmt.Printf("longCalculation took this amount of time: %s\n", delta)
+}