add: marshaler interface

interfaces/10-marshaler/_decoder.go

@@ -0,0 +1,60 @@
+// 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"
+	"reflect"
+)
+
+type decoder map[string]interface{}
+
+type schema struct {
+	Category string
+	Item     json.RawMessage
+}
+
+func (d decoder) decode(data []byte) (list, error) {
+	var schemas []schema
+
+	if err := json.Unmarshal(data, &schemas); err != nil {
+		return nil, err
+	}
+
+	return d.products(schemas)
+}
+
+func (d decoder) products(ss []schema) (list, error) {
+	var store list
+
+	for _, s := range ss {
+		prod, err := d.product(s.Category, s.Item)
+
+		if err != nil {
+			return nil, err
+		}
+
+		store = append(store, prod)
+	}
+
+	return store, nil
+}
+
+func (d decoder) product(kind string, data []byte) (item, error) {
+	p := d.newProduct(kind)
+
+	err := json.Unmarshal(data, p)
+
+	return p, err
+}
+
+func (d decoder) newProduct(kind string) item {
+	t := reflect.TypeOf(d[kind])
+	v := reflect.New(t)
+	return v.Interface().(item)
+}

interfaces/10-marshaler/_decoder_reader.go

@@ -0,0 +1,85 @@
+// 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"
+	"io"
+	"io/ioutil"
+	"os"
+	"reflect"
+)
+
+type decoder map[string]interface{}
+
+type schema struct {
+	Category string
+	Item     json.RawMessage
+}
+
+func (d decoder) fromFile(path string) (list, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return d.readFile(f)
+}
+
+func (d decoder) readFile(f *os.File) (list, error) {
+	return d.read(f)
+}
+
+func (d decoder) read(r io.Reader) (list, error) {
+	data, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	return d.decode(data)
+}
+
+func (d decoder) decode(data []byte) (list, error) {
+	var schemas []schema
+
+	if err := json.Unmarshal(data, &schemas); err != nil {
+		return nil, err
+	}
+
+	return d.products(schemas)
+}
+
+func (d decoder) products(ss []schema) (list, error) {
+	var store list
+
+	for _, s := range ss {
+		prod, err := d.product(s.Category, s.Item)
+
+		if err != nil {
+			return nil, err
+		}
+
+		store = append(store, prod)
+	}
+
+	return store, nil
+}
+
+func (d decoder) product(kind string, data []byte) (item, error) {
+	p := d.newProduct(kind)
+
+	err := json.Unmarshal(data, p)
+
+	return p, err
+}
+
+func (d decoder) newProduct(kind string) item {
+	t := reflect.TypeOf(d[kind])
+	v := reflect.New(t)
+	return v.Interface().(item)
+}

interfaces/10-marshaler/_main.go

@@ -0,0 +1,42 @@
+// 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"
+	"io/ioutil"
+	"log"
+	"os"
+)
+
+func main() {
+	dec := make(decoder)
+	dec["book"] = book{}
+	dec["game"] = game{}
+	dec["puzzle"] = puzzle{}
+	dec["toy"] = toy{}
+
+	data, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	store, err := dec.decode(data)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Print(store)
+
+	// store.discount(.5)
+	// fmt.Print(store)
+
+	// ----
+	// data, err := save(store)
+	// fmt.Println(string(data), err)
+}

interfaces/10-marshaler/_main_reader.go

@@ -0,0 +1,30 @@
+// 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"
+	"log"
+	"os"
+)
+
+func main() {
+	dec := decoder{
+		"book":   book{},
+		"game":   game{},
+		"puzzle": puzzle{},
+		"toy":    toy{},
+	}
+
+	store, err := dec.read(os.Stdin)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Print(store)
+}

interfaces/10-marshaler/book.go

@@ -0,0 +1,64 @@
+// 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"
+	"strconv"
+	"time"
+)
+
+type book struct {
+	product
+	Published interface{}
+}
+
+func (b book) String() string {
+	p := format(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/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
+}

interfaces/10-marshaler/list.go

@@ -0,0 +1,70 @@
+// 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"
+	"reflect"
+	"strings"
+)
+
+type item interface {
+	discount(float64)
+	fmt.Stringer
+}
+
+// schema adds an additional category field
+// to the product types.
+type schema struct {
+	// Category is the product category field.
+	Category string
+
+	// Item is an interface value.
+	// Here, we are embedding an interface value.
+	Item item
+}
+
+type list []item
+
+// MarshalJSON is an implementation of the json.Marshaler interface.
+// json.Marshal and Decode call this method.
+func (l list) MarshalJSON() ([]byte, error) {
+	var schemas []schema
+
+	for _, it := range l {
+		// TypeOf -> finds the dynamic type of "it"
+		// Elem   -> returns the element type of the pointer
+		// Name   -> returns the type name as string
+		cat := reflect.TypeOf(it).Elem().Name()
+		schemas = append(schemas, schema{cat, it})
+	}
+
+	return json.Marshal(schemas)
+}
+
+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)
+	}
+}

interfaces/10-marshaler/main.go

@@ -0,0 +1,35 @@
+// 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"
+)
+
+func main() {
+	store := list{
+		&book{product{"moby dick", 10}, 118281600},
+		&book{product{"odyssey", 15}, "733622400"},
+		&book{product{"hobbit", 25}, nil},
+		&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)
+}

interfaces/10-marshaler/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/10-marshaler/product.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 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)
+}

interfaces/10-marshaler/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
+}

interfaces/10-marshaler/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
+}