interfaces: refactor

interfaces/04-interfaces/list.go

@@ -0,0 +1,71 @@
+// 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"
+
+// TODO: NEW
+type printer interface {
+	print()
+}
+
+// TODO: NEW
+type pricer interface {
+	total() float64
+}
+
+// TODO: NEW
+// interface embedding
+type item interface {
+	printer
+	pricer
+}
+
+// a slice of item interface values
+type list []item
+
+func (l list) list() {
+	// `list` acts like a `[]game`
+	if len(l) == 0 {
+		fmt.Println("Sorry. Our store is closed. We're waiting for the delivery 🚚.")
+		return
+	}
+
+	fmt.Printf("My Store:\n")
+	fmt.Printf("---------\n")
+	for _, it := range l {
+		it.print()
+	}
+
+	// TODO: NEW
+	fmt.Printf("\nGROSS: $%.2f\n", l.total())
+}
+
+// TODO: NEW
+func (l list) total() (gross float64) {
+	for _, it := range l {
+		gross += it.total()
+	}
+	return gross
+}
+
+// TODO: NEW
+func (l list) discount(ratio float64) {
+	type discounter interface {
+		discount(float64)
+	}
+
+	for _, it := range l {
+		dit, ok := it.(discounter)
+		if !ok {
+			continue
+		}
+
+		dit.discount(ratio)
+	}
+}