refactor: stringer interface

interfaces/09-stringer/book.go

@@ -9,43 +9,20 @@ package main
 
 import (
 	"fmt"
-	"strconv"
-	"time"
 )
 
 type book struct {
 	product
-	published interface{}
+	published timestamp
 }
 
 // book satisfies the fmt.Stringer
 func (b *book) String() string {
-	p := format(b.published)
-
 	// product.String() has a pointer receiver.
 	// That's why you need to manually take the product's address here.
 	//
 	// If you pass: "b.product", Go would pass it as a copy to Sprintf.
 	// In that case, Go can't deference b.product automatically.
 	// It's because: b.product would be different value—a copy.
-	return fmt.Sprintf("%s - (%v)", &b.product, p)
+	return fmt.Sprintf("%s - (%s)", &b.product, b.published)
-}
-
-func format(v interface{}) string {
-	var t int
-
-	switch v := v.(type) {
-	case int:
-		t = v
-	case string:
-		t, _ = strconv.Atoi(v)
-	default:
-		return "unknown"
-	}
-
-	// Mon Jan 2 15:04:05 -0700 MST 2006
-	const layout = "2006/01"
-
-	u := time.Unix(int64(t), 0)
-	return u.Format(layout)
 }

interfaces/09-stringer/main.go

@@ -11,9 +11,9 @@ import "fmt"
 
 func main() {
 	store := list{
-		&book{product{"moby dick", 10}, 118281600},
+		&book{product{"moby dick", 10}, toTimestamp(118281600)},
-		&book{product{"odyssey", 15}, "733622400"},
+		&book{product{"odyssey", 15}, toTimestamp("733622400")},
-		&book{product{"hobbit", 25}, nil},
+		&book{product{"hobbit", 25}, unknown},
 		&puzzle{product{"rubik's cube", 5}},
 		&game{product{"minecraft", 20}},
 		&game{product{"tetris", 5}},
@@ -26,4 +26,8 @@ func main() {
 	// but the Print function can print it.
 	// it's because, the list satisfies the stringer.
 	fmt.Print(store)
+
+	// timestamp is useful even if it's zero.
+	var ts timestamp
+	fmt.Println(ts)
 }

interfaces/09-stringer/timestamp.go

@@ -0,0 +1,51 @@
+// 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.
+// Timestamp is useful even if it's zero.
+type timestamp time.Time
+
+// String makes the timestamp a stringer.
+func (ts timestamp) String() string {
+	t := time.Time(ts)
+
+	if t.IsZero() {
+		return "unknown"
+	}
+
+	return t.Format(layout)
+}
+
+// toTimestamp was "book.format" before.
+// Now it returns a timestamp value depending on the type of `v`.
+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))
+}

interfaces/10-marshaler/book.go

@@ -8,57 +8,14 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
-	"strconv"
-	"time"
 )
 
 type book struct {
 	product
-	Published interface{}
+	Published timestamp
 }
 
 func (b book) String() string {
-	p := format(b.Published)
+	return fmt.Sprintf("%s - (%s)", &b.product, b.Published)
-	return fmt.Sprintf("%s - (%v)", &b.product, p)
-}
-
-// MarshalJSON is an implementation of the json.Marshaler interface.
-// json.Marshal and Decode call this method.
-func (b *book) MarshalJSON() ([]byte, error) {
-	// Calling Marshal creates an infinite loop because Marshal calls
-	// MarshalJSON again and again.
-	//
-	// Declaring a clone type without MarshalJSON fixes the problem.
-	type jbook book
-
-	// book is convertable to jbook
-	// jbook's underlying type is book.
-	jb := (*jbook)(b)
-
-	// Customize the formatting of the published field.
-	// This will result in the published field of the resulting json.
-	jb.Published = format(b.Published)
-
-	return json.Marshal(jb)
-}
-
-func format(v interface{}) string {
-	var t int
-
-	switch v := v.(type) {
-	case int:
-		t = v
-	case string:
-		t, _ = strconv.Atoi(v)
-	default:
-		return "unknown"
-	}
-
-	// Mon Jan 2 15:04:05 -0700 MST 2006
-	const layout = "2006/01"
-
-	u := time.Unix(int64(t), 0)
-	return u.Format(layout)
 }

interfaces/10-marshaler/main.go

@@ -14,22 +14,85 @@ import (
 )
 
 func main() {
-	store := list{
+	// store := list{
-		&book{product{"moby dick", 10}, 118281600},
+	// 	&book{product{"moby dick", 10}, 118281600},
-		&book{product{"odyssey", 15}, "733622400"},
+	// 	&book{product{"odyssey", 15}, "733622400"},
-		&book{product{"hobbit", 25}, nil},
+	// 	&book{product{"hobbit", 25}, nil},
-		&puzzle{product{"rubik's cube", 5}},
+	// 	&puzzle{product{"rubik's cube", 5}},
-		&game{product{"minecraft", 20}},
+	// 	&game{product{"minecraft", 20}},
-		&game{product{"tetris", 5}},
+	// 	&game{product{"tetris", 5}},
-		&toy{product{"yoda", 150}},
+	// 	&toy{product{"yoda", 150}},
-	}
+	// }
 
-	out, err := json.MarshalIndent(store, "", "\t")
+	// out, err := json.MarshalIndent(store, "", "\t")
-	if err != nil {
+	// if err != nil {
-		log.Fatalln(err)
+	// 	log.Fatalln(err)
-	}
+	// }
-	fmt.Println(string(out))
+	// fmt.Println(string(out))
 
 	// store.discount(.5)
 	// fmt.Print(store)
+
+	encode()
+}
+
+func encode() {
+
+	books := []*book{
+		{product{"moby dick", 10}, toTime(118281600)},
+		{product{"odyssey", 15}, toTime("733622400")},
+		{product{"hobbit", 25}, zeroTimestamp},
+	}
+
+	for _, b := range books {
+		fmt.Println(b)
+	}
+
+	out, err := json.MarshalIndent(books, "", "\t")
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Println(string(out))
+}
+
+func decode() {
+	// books = nil
+	out := []byte(`[
+	{
+		"Title": "moby dick",
+		"Price": 10,
+		"Published": "118281600"
+	},
+	{
+		"Title": "odyssey",
+		"Price": 15,
+		"Published": 733622400
+	},
+	{
+		"Title": "hobbit",
+		"Price": 25,
+		"Published": -62135596800
+	},
+	{
+		"Title": "poka",
+		"Price": 25,
+		"Published": "1983/03"
+	},
+	{
+		"Title": "fuka",
+		"Price": 25
+	}	
+]`)
+
+	var books []*book
+
+	err := json.Unmarshal(out, &books)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	for _, b := range books {
+		fmt.Println(b)
+	}
 }