add: type switch

interfaces/08-composition/book.go

@@ -0,0 +1,25 @@
+// 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    money
+	readTime int
+}
+
+func (b book) print() {
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
+}
+
+// TODO: NEW
+func (b book) sum() money {
+	return b.price
+}

interfaces/08-composition/discount.go

@@ -0,0 +1,17 @@
+package main
+
+// usually: include the discount method in the list.go
+// it is here for clarity
+
+// TODO: NEW
+func (l list) discount(ratio float64) {
+	type discounter interface {
+		discount(float64)
+	}
+
+	for _, it := range l {
+		if it, ok := it.(discounter); ok {
+			it.discount(ratio)
+		}
+	}
+}

interfaces/08-composition/game.go

@@ -0,0 +1,33 @@
+// 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    money
+	playTime int
+}
+
+func (g *game) print() {
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
+}
+
+// func (g *game) String() string {
+// 	return fmt.Sprintf("%-15s: $%.2f", g.title, g.price)
+// }
+
+func (g *game) discount(ratio float64) {
+	g.price *= money(1 - ratio)
+}
+
+// TODO: NEW
+func (g *game) sum() money {
+	return g.price
+}

interfaces/08-composition/list.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 list []item
+
+func (l list) print() {
+	if len(l) == 0 {
+		fmt.Println("Sorry. Our store is closed. We're waiting for the delivery 🚚.")
+		return
+	}
+
+	for _, it := range l {
+		it.print()
+	}
+
+	// TODO: NEW
+	fmt.Printf("\tTOTAL  : $%.2f\n", l.sum())
+}
+
+// TODO: NEW
+func (l list) sum() (n money) {
+	for _, it := range l {
+		n += it.sum()
+	}
+	return n
+}

interfaces/08-composition/main.go

@@ -0,0 +1,43 @@
+// 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"
+
+func main() {
+	var (
+		mobydick  = book{title: "moby dick", price: 10, readTime: 10}
+		minecraft = game{title: "minecraft", price: 20, playTime: 5}
+		tetris    = game{title: "tetris", price: 5, playTime: 2}
+		rubik     = puzzle{title: "rubik's cube", price: 5}
+	)
+
+	var store list
+	store = append(store, &minecraft, &tetris, mobydick, rubik)
+	// tetris.discount(.8)
+	// store.print()
+
+	store.discount(.5)
+	store.print()
+
+	// t := store.time()
+	// fmt.Printf("Total entertainment time: %d hours\n", t)
+
+	// games := store[:2]
+	// other := store[2:]
+	// games.print()
+	// other.print()
+	// list{games, other}.print()
+
+	// var b *book
+
+	// var np printer
+	// np = b
+	// // p := printer(puzzle{title: "sidewinder", price: 10})
+	// fmt.Println(np == nil)
+}

interfaces/08-composition/money.go

@@ -0,0 +1,16 @@
+// 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 money float64
+
+func (m money) string() string {
+	return fmt.Sprintf("$%.2f", m)
+}

interfaces/08-composition/puzzle.go

@@ -0,0 +1,24 @@
+// 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 puzzle struct {
+	title string
+	price money
+}
+
+func (p puzzle) print() {
+	fmt.Printf("%-15s: %s\n", p.title, p.price.string())
+}
+
+// TODO: NEW
+func (p puzzle) sum() money {
+	return p.price
+}

interfaces/08-composition/time.go

@@ -0,0 +1,19 @@
+package main
+
+// usually: include the time method in the list.go
+// it is here for clarity
+
+// TODO: NEW
+// you could include a time method in the book and game instead.
+// but sometimes it is not possible to do so.
+func (l list) time() (total int) {
+	for _, it := range l {
+		switch it := it.(type) {
+		case *game:
+			total += it.playTime
+		case book:
+			total += it.readTime
+		}
+	}
+	return total
+}

interfaces/08-composition/types.go

@@ -0,0 +1,23 @@
+package main
+
+// don't separate your interfaces like this.
+// put them in the same file where you need to use them.
+// this is here for clarity
+
+type printer interface {
+	print()
+}
+
+// TODO: NEW
+type summer interface {
+	sum() money
+}
+
+// TODO: NEW
+// interface embedding
+// When an interface includes multiple methods,
+// choose a name that accurately describes its purpose.
+type item interface {
+	printer
+	summer
+}