add: type switch

interfaces/08-composition/list.go

@@ -0,0 +1,34 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+type list []item
+
+func (l list) print() {
+	if len(l) == 0 {
+		fmt.Println("Sorry. Our store is closed. We're waiting for the delivery 🚚.")
+		return
+	}
+
+	for _, it := range l {
+		it.print()
+	}
+
+	// TODO: NEW
+	fmt.Printf("\tTOTAL  : $%.2f\n", l.sum())
+}
+
+// TODO: NEW
+func (l list) sum() (n money) {
+	for _, it := range l {
+		n += it.sum()
+	}
+	return n
+}