reorganize: interfaces section

interfaces/02-receivers/game.go

@@ -14,6 +14,9 @@ type game struct {
 	price float64
 }
 
+// be consistent:
+// if another method in the same type has a pointer receiver,
+// use pointer receivers on the other methods as well.
 func (g *game) print() {
 	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
 }
@@ -27,8 +30,7 @@ func (g *game) discount(ratio float64) {
 
 // PREVIOUS CODE:
 
-// ----------------------------------------------------------------------------
 // + `g` is a copy: `discount` cannot change the original `g`.
-// func (g game) discount(ratio float64) {
+// func (g *game) discount(ratio float64) {
 // 	g.price *= (1 - ratio)
 // }