interfaces: refactor

interfaces/02-receivers/book.go

@@ -0,0 +1,20 @@
+// 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 book struct {
+	title string
+	price float64
+}
+
+func (b book) print() {
+	// b is a copy of the original `book` value here.
+	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+}

interfaces/02-receivers/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)
+// }

interfaces/02-receivers/list.go

@@ -0,0 +1,28 @@
+// 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"
+
+// + you can attach methods to any concrete type.
+// + rule: you need to declare a new type in the same package.
+type list []game
+
+func (l list) print() {
+	// `list` acts like a `[]game`
+	if len(l) == 0 {
+		fmt.Println("Sorry. Our store is closed. We're waiting for the delivery 🚚.")
+		return
+	}
+
+	fmt.Printf("My Store:\n")
+	fmt.Printf("---------\n")
+	for _, it := range l {
+		it.print()
+	}
+}

interfaces/02-receivers/main.go

@@ -0,0 +1,27 @@
+// 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
+
+func main() {
+	var (
+		// mobydick  = book{title: "moby dick", price: 10}
+		minecraft = game{title: "minecraft", price: 20}
+		tetris    = game{title: "tetris", price: 5}
+	)
+
+	var items []game
+	items = append(items, minecraft, tetris)
+
+	// you can attach methods to a compatible type on the fly:
+	my := list([]game{minecraft, tetris})
+
+	// you can call methods even on a nil value
+	// my = nil
+
+	my.print() // or: list.print(items)
+}