update: interfaces

interfaces/03-interfaces/book.go

@@ -15,6 +15,5 @@ type book struct {
 }
 
 func (b book) print() {
-	// b is a copy of the original `book` value here.
 	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
 }

interfaces/03-interfaces/game.go

@@ -18,17 +18,6 @@ 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)
-// }
+}

interfaces/03-interfaces/list.go

@@ -21,8 +21,6 @@ func (l list) print() {
 		return
 	}
 
-	fmt.Printf("My Store:\n")
-	fmt.Printf("---------\n")
 	for _, it := range l {
 		it.print()
 

interfaces/03-interfaces/main.go

@@ -16,37 +16,18 @@ func main() {
 	)
 
 	var store list
-
 	store = append(store, &minecraft, &tetris, mobydick, rubik)
 
 	tetris.discount(.8)
 	// printer(tetris).discount(.8)
-
 	store.print()
-}
 
-/*
-var my list
+	// type printer interface {
+	// 	print()
+	// }
 
-// + only the `*game` have methods.
-// + `game` doesn't have any methods.
-// + `item` interface couldn't be satisfied with a `game` value.
-// + it can only be satisfied with a `*game` value.
-// my = my.add(minecraft)
-my = append(my, &minecraft)
-my = append(my, &tetris)
-my = append(my, &mobydick)
-
-// interface value stores a pointer to minecraft
-minecraft.discount(.5)
-my.list()
-
-my.discount(.5)
-my.list()
-*/
-
-// ! cannot add mobydick to the store: it's a book type, not a game type.
-// interfaces to the rescue!
-// mobydick := book{title: "moby dick", price: 10}
-// my.add(&mobydick)
-// ----------------------------------------------------------------
+	// p can store a value of any type that has a `print()` method
+	var p printer
+	p = puzzle{title: "sidewinder", price: 10}
+	p.print()
+}