add: type assertion

interfaces/05-assertion/toy.go

@@ -0,0 +1,23 @@
+// 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 toy struct {
+	title string
+	price money
+}
+
+func (t *toy) print() {
+	fmt.Printf("%-15s: %s\n", t.title, t.price.string())
+}
+
+func (t *toy) discount(ratio float64) {
+	t.price *= money(1 - ratio)
+}