refactor: common ifaces

interfaces/12-marshaler/product.go

@@ -0,0 +1,26 @@
+// 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 product struct {
+	Title    string    `json:"title"`
+	Price    money     `json:"price"`
+	Released timestamp `json:"released,omitempty"`
+}
+
+func (p *product) String() string {
+	return fmt.Sprintf("%s: %s (%s)", p.Title, p.Price, p.Released)
+}
+
+func (p *product) discount(ratio float64) {
+	p.Price *= money(1 - ratio)
+}