diff --git a/interfaces/11-decode-toiface/book.go b/interfaces/11-decode-toiface/book.go
new file mode 100644
index 0000000..c36372f
--- /dev/null
+++ b/interfaces/11-decode-toiface/book.go
@@ -0,0 +1,21 @@
+// 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 {
+	product
+	Published timestamp
+}
+
+func (b *book) String() string {
+	return fmt.Sprintf("%s - (%s)", &b.product, b.Published)
+}
diff --git a/interfaces/11-decode-toiface/database.go b/interfaces/11-decode-toiface/database.go
new file mode 100644
index 0000000..f09209e
--- /dev/null
+++ b/interfaces/11-decode-toiface/database.go
@@ -0,0 +1,56 @@
+// 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 (
+	"encoding/json"
+	"fmt"
+	"log"
+)
+
+type database struct {
+	list *list
+}
+
+func (db *database) UnmarshalJSON(data []byte) error {
+	var decodables []struct {
+		Type string
+		Item json.RawMessage
+	}
+
+	if err := json.Unmarshal(data, &decodables); err != nil {
+		log.Fatalln(err)
+	}
+
+	for _, d := range decodables {
+		it, err := db.newItem(d.Item, d.Type)
+		if err != nil {
+			return err
+		}
+
+		*db.list = append(*db.list, it)
+	}
+
+	return nil
+}
+
+func (db *database) newItem(data []byte, itemType string) (it item, _ error) {
+	switch itemType {
+	default:
+		return nil, fmt.Errorf("newItem: type (%q) does not exist", itemType)
+	case "book":
+		it = new(book)
+	case "puzzle":
+		it = new(puzzle)
+	case "game":
+		it = new(game)
+	case "toy":
+		it = new(toy)
+	}
+	return it, json.Unmarshal(data, &it)
+}
diff --git a/interfaces/11-decode-toiface/database.json b/interfaces/11-decode-toiface/database.json
new file mode 100644
index 0000000..cccab62
--- /dev/null
+++ b/interfaces/11-decode-toiface/database.json
@@ -0,0 +1,54 @@
+[
+	{
+		"Type": "book",
+		"Item": {
+			"Title": "moby dick",
+			"Price": 10,
+			"Published": 118281600
+		}
+	},
+	{
+		"Type": "book",
+		"Item": {
+			"Title": "odyssey",
+			"Price": 15,
+			"Published": 733622400
+		}
+	},
+	{
+		"Type": "book",
+		"Item": {
+			"Title": "hobbit",
+			"Price": 25,
+			"Published": -62135596800
+		}
+	},
+	{
+		"Type": "puzzle",
+		"Item": {
+			"Title": "rubik's cube",
+			"Price": 5
+		}
+	},
+	{
+		"Type": "game",
+		"Item": {
+			"Title": "minecraft",
+			"Price": 20
+		}
+	},
+	{
+		"Type": "game",
+		"Item": {
+			"Title": "tetris",
+			"Price": 5
+		}
+	},
+	{
+		"Type": "toy",
+		"Item": {
+			"Title": "yoda",
+			"Price": 150
+		}
+	}
+]
diff --git a/interfaces/11-decode-toiface/game.go b/interfaces/11-decode-toiface/game.go
new file mode 100644
index 0000000..3604b15
--- /dev/null
+++ b/interfaces/11-decode-toiface/game.go
@@ -0,0 +1,12 @@
+// 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
+
+type game struct {
+	product
+}
diff --git a/interfaces/11-decode-toiface/list.go b/interfaces/11-decode-toiface/list.go
new file mode 100644
index 0000000..69da963
--- /dev/null
+++ b/interfaces/11-decode-toiface/list.go
@@ -0,0 +1,40 @@
+// 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"
+	"strings"
+)
+
+type item interface {
+	discount(float64)
+	fmt.Stringer
+}
+
+type list []item
+
+func (l list) String() string {
+	if len(l) == 0 {
+		return "Sorry. We're waiting for delivery 🚚."
+	}
+
+	var str strings.Builder
+	for _, it := range l {
+		str.WriteString(it.String())
+		str.WriteRune('\n')
+	}
+
+	return str.String()
+}
+
+func (l list) discount(ratio float64) {
+	for _, it := range l {
+		it.discount(ratio)
+	}
+}
diff --git a/interfaces/11-decode-toiface/main.go b/interfaces/11-decode-toiface/main.go
new file mode 100644
index 0000000..5aae9cc
--- /dev/null
+++ b/interfaces/11-decode-toiface/main.go
@@ -0,0 +1,54 @@
+// 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 (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+)
+
+func main() {
+	data, err := ioutil.ReadFile("database.json")
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	var store list
+
+	db := database{list: &store}
+
+	if err := json.Unmarshal(data, &db); err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Print(store)
+
+	/*
+		store := list{
+			&book{product{"moby dick", 10}, toTimestamp(118281600)},
+			&book{product{"odyssey", 15}, toTimestamp("733622400")},
+			&book{product{"hobbit", 25}, unknown},
+			&puzzle{product{"rubik's cube", 5}},
+			&game{product{"minecraft", 20}},
+			&game{product{"tetris", 5}},
+			&toy{product{"yoda", 150}},
+		}
+
+		out, err := json.MarshalIndent(store, "", "\t")
+		if err != nil {
+			log.Fatalln(err)
+		}
+
+		fmt.Println(string(out))
+
+		// store.discount(.5)
+		// fmt.Print(store)
+	*/
+}
diff --git a/interfaces/11-decode-toiface/money.go b/interfaces/11-decode-toiface/money.go
new file mode 100644
index 0000000..095a039
--- /dev/null
+++ b/interfaces/11-decode-toiface/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)
+}
diff --git a/interfaces/11-decode-toiface/product.go b/interfaces/11-decode-toiface/product.go
new file mode 100644
index 0000000..f93cb84
--- /dev/null
+++ b/interfaces/11-decode-toiface/product.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 product struct {
+	Title string
+	Price money
+}
+
+func (p *product) String() string {
+	return fmt.Sprintf("%-15s: %s", p.Title, p.Price)
+}
+
+func (p *product) discount(ratio float64) {
+	p.Price *= money(1 - ratio)
+}
diff --git a/interfaces/11-decode-toiface/puzzle.go b/interfaces/11-decode-toiface/puzzle.go
new file mode 100644
index 0000000..acbaa47
--- /dev/null
+++ b/interfaces/11-decode-toiface/puzzle.go
@@ -0,0 +1,12 @@
+// 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
+
+type puzzle struct {
+	product
+}
diff --git a/interfaces/11-decode-toiface/timestamp.go b/interfaces/11-decode-toiface/timestamp.go
new file mode 100644
index 0000000..28629d8
--- /dev/null
+++ b/interfaces/11-decode-toiface/timestamp.go
@@ -0,0 +1,77 @@
+// 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 (
+	"strconv"
+	"time"
+)
+
+// Mon Jan 2 15:04:05 -0700 MST 2006
+const layout = "2006/01"
+
+// unknown is the zero value of a timestamp.
+var unknown = timestamp(time.Time{})
+
+// timestamp prints timestamps, it's a stringer.
+// It is useful even if it's zero.
+type timestamp time.Time
+
+// MarshalJSON from timestamp.
+func (ts timestamp) MarshalJSON() (out []byte, err error) {
+	u := time.Time(ts).Unix()
+	return strconv.AppendInt(out, u, 10), nil
+}
+
+// UnmarshalJSON data to timestamp.
+func (ts *timestamp) UnmarshalJSON(data []byte) error {
+	s := string(data)
+
+	// Let the ParseInt parse quoted strings.
+	us, err := strconv.Unquote(s)
+	if err == nil {
+		s = us
+	}
+
+	// Always overwrite the timestamp when decoding.
+	*ts = unknown
+
+	// Handle the numeric case.
+	if n, err := strconv.ParseInt(s, 10, 64); err == nil {
+		*ts = timestamp(time.Unix(n, 0))
+	}
+
+	return nil
+}
+
+// String representation of the timestamp.
+func (ts timestamp) String() string {
+	t := time.Time(ts)
+
+	if t.IsZero() {
+		return "unknown"
+	}
+
+	return t.Format(layout)
+}
+
+// toTimestamp from an unknown value.
+func toTimestamp(v interface{}) timestamp {
+	var t int
+
+	switch v := v.(type) {
+	case int:
+		t = v
+	case string:
+		t, _ = strconv.Atoi(v)
+	default:
+		return unknown
+	}
+
+	return timestamp(time.Unix(int64(t), 0))
+}
diff --git a/interfaces/11-decode-toiface/toy.go b/interfaces/11-decode-toiface/toy.go
new file mode 100644
index 0000000..ab5613d
--- /dev/null
+++ b/interfaces/11-decode-toiface/toy.go
@@ -0,0 +1,12 @@
+// 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
+
+type toy struct {
+	product
+}