reorganize: interfaces section

interfaces/03-nonstructs/game.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 game struct {
+	title string
+	price float64
+}
+
+func (g *game) print() {
+	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
+}
+
+// + discount gets a copy of `*game`.
+// + discount can update the original `game` through the game pointer.
+// + it's better to use the same receiver type: `*game` for all methods.
+func (g *game) discount(ratio float64) {
+	g.price *= (1 - ratio)
+}
+
+// PREVIOUS CODE:
+
+// ----------------------------------------------------------------------------
+// + `g` is a copy: `discount` cannot change the original `g`.
+// func (g game) discount(ratio float64) {
+// 	g.price *= (1 - ratio)
+// }