add: type switch

interfaces/06-empty-interface/book.go

@@ -0,0 +1,47 @@
+// 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"
+	"strconv"
+	"time"
+)
+
+type book struct {
+	title     string
+	price     money
+	published interface{}
+}
+
+func (b book) print() {
+	p := format(b.published)
+	fmt.Printf("%-15s: %s - (%v)\n", b.title, b.price.string(), p)
+}
+
+func format(v interface{}) string {
+	// book{title: "hobbit", price: 25},
+	if v == nil {
+		return "unknown"
+	}
+
+	var t int
+
+	// book{title: "moby dick", price: 10, published: 118281600},
+	if v, ok := v.(int); ok {
+		t = v
+	}
+
+	// book{title: "odyssey", price: 15, published: "733622400"},
+	if v, ok := v.(string); ok {
+		t, _ = strconv.Atoi(v)
+	}
+
+	u := time.Unix(int64(t), 0)
+	return u.String()
+}

interfaces/06-empty-interface/empty/main.go

@@ -0,0 +1,29 @@
+// 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() {
+	// Let's create a variable using the empty interface type.
+	var any interface{}
+
+	// The variable can accept any type of value.
+	any = []int{1, 2, 3}
+	any = map[int]bool{1: true, 2: false}
+	any = "hello"
+	any = 3
+
+	// You can't multiply the last number.
+	// Reason: `any` is an `interface{}`, it's not a number.
+	// any = any * 2
+	// any = int(any) * 2
+
+	any = any.(int) * 2
+	fmt.Println(any)
+}

interfaces/06-empty-interface/empty2/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() {
+	nums := []int{1, 2, 3}
+
+	// Store a slice in `any`
+	var any interface{}
+	any = nums
+
+	// `any` is an empty interface value, it's not a slice.
+	// You cannot get its length. It has no length.
+	// _ = len(any)
+
+	// When you extract the slice from it, you can get the slice's length.
+	_ = len(any.([]int))
+
+	// You cannot assign an `[]T` slice to `[]interface{}` slice.
+	// Where `T` can be of any type.
+	// Reason: `[]interface{}` is a slice, it's not an `empty interface` value.
+	var many []interface{}
+	// many = nums
+
+	// The same reason that you can't assign an `[]int` to a `[]string`.
+	// var words []string = nums
+
+	// You need to copy the elements from `nums` to `many` manually.
+	for _, n := range nums {
+		many = append(many, n)
+	}
+	fmt.Println(many)
+
+	// Each element of the `many` slice is an `empty interface` value.
+	// el := many[0]
+}

interfaces/06-empty-interface/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/06-empty-interface/list.go

@@ -0,0 +1,39 @@
+// 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()
+}
+
+type list []printer
+
+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()
+	}
+}
+
+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/06-empty-interface/main.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
+
+func main() {
+	store := list{
+		book{title: "moby dick", price: 10, published: 118281600},
+		book{title: "odyssey", price: 15, published: "733622400"},
+		book{title: "hobbit", price: 25},
+		puzzle{title: "rubik's cube", price: 5},
+		&game{title: "minecraft", price: 20},
+		&game{title: "tetris", price: 5},
+		&toy{title: "yoda", price: 150},
+	}
+
+	store.discount(.5)
+	store.print()
+}

interfaces/06-empty-interface/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/06-empty-interface/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/06-empty-interface/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)
+}