rename: interfaces type assertion

interfaces/05-type-assertion/book.go

@@ -0,0 +1,19 @@
+// 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
+}
+
+func (b book) print() {
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
+}

interfaces/05-type-assertion/game.go

@@ -0,0 +1,23 @@
+// 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
+}
+
+func (g *game) print() {
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
+}
+
+func (g *game) discount(ratio float64) {
+	g.price *= money(1 - ratio)
+}

interfaces/05-type-assertion/list.go

@@ -0,0 +1,78 @@
+// 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 printer interface {
+	print()
+
+	// use type assertion when you cannot change the interface.
+	// discount(ratio float64)
+}
+
+type list []printer
+
+func (l list) print() {
+	if len(l) == 0 {
+		fmt.Println("Sorry. We're waiting for delivery 🚚.")
+		return
+	}
+
+	for _, it := range l {
+		it.print()
+	}
+}
+
+// type assertion can extract the wrapped value.
+// or: it can put the value into another interface.
+func (l list) discount(ratio float64) {
+	// you can declare an interface in a function/method as well.
+	// interface is just a type.
+	type discounter interface {
+		discount(float64)
+	}
+
+	for _, it := range l {
+		// you can assert to an interface.
+		// and extract another interface.
+		if it, ok := it.(discounter); ok {
+			it.discount(ratio)
+		}
+	}
+}
+
+// ----
+
+// func (l list) discount(ratio float64) {
+// 	for _, it := range l {
+// 		// you can inline-assert interfaces
+// 		// interface is just a type.
+// 		g, ok := it.(interface{ discount(float64) })
+// 		if !ok {
+// 			continue
+// 		}
+
+// 		g.discount(ratio)
+// 	}
+// }
+
+// ----
+
+// // type assertion can pull out the real value behind an interface value.
+// // it can also check whether the value convertable to a given type.
+// func (l list) discount(ratio float64) {
+// 	for _, it := range l {
+// 		g, ok := it.(*game)
+// 		if !ok {
+// 			continue
+// 		}
+
+// 		g.discount(ratio)
+// 	}
+// }

interfaces/05-type-assertion/main.go

@@ -0,0 +1,31 @@
+// 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}
+		rubik     = puzzle{title: "rubik's cube", price: 5}
+		yoda      = toy{title: "yoda", price: 150}
+	)
+
+	var store list
+	store = append(store, &minecraft, &tetris, mobydick, rubik, &yoda)
+
+	// #2
+	store.discount(.5)
+	store.print()
+
+	// #1
+	// var p printer
+	// p = &tetris
+	// tetris.discount(.5)
+	// p.print()
+}

interfaces/05-type-assertion/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/05-type-assertion/puzzle.go

@@ -0,0 +1,19 @@
+// 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())
+}

interfaces/05-type-assertion/toy.go

@@ -0,0 +1,23 @@
+// 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 toy struct {
+	title string
+	price money
+}
+
+func (t *toy) print() {
+	fmt.Printf("%-15s: %s\n", t.title, t.price.string())
+}
+
+func (t *toy) discount(ratio float64) {
+	t.price *= money(1 - ratio)
+}