update book code

eBook/examples/chapter_11/print.go

@@ -0,0 +1,43 @@
+// print.go
+package main
+
+import (
+	"os"
+	"strconv"
+)
+
+type Stringer interface {
+	String() string
+}
+
+type Celsius float64
+
+func (c Celsius) String() string {
+	return strconv.FormatFloat(float64(c),'f', 1, 64) + " °C"
+}
+
+type Day int
+
+var dayName = []string{"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"}
+
+func (day Day) String() string {
+	return dayName[day]
+}
+
+func print(args ...interface{}) {
+	for i, arg := range args {
+		if i > 0 {os.Stdout.WriteString(" ")}
+		switch a := arg.(type) { // type switch
+			case Stringer:	os.Stdout.WriteString(a.String())
+			case int:		os.Stdout.WriteString(strconv.Itoa(a))
+			case string:	os.Stdout.WriteString(a)
+			// more types
+			default:		os.Stdout.WriteString("???")
+		}
+	}
+}
+
+func main() {
+	print(Day(1), "was", Celsius(18.36))  // Tuesday was 18.4 °C
+}
+// Tuesday was 18.4 °C