refactor: common ifaces

interfaces/09-little-refactor/list.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"
+
+type list []*product
+
+func (l list) print() {
+	if len(l) == 0 {
+		fmt.Println("Sorry. We're waiting for delivery 🚚.")
+		return
+	}
+
+	for _, p := range l {
+		p.print()
+	}
+}
+
+func (l list) discount(ratio float64) {
+	for _, p := range l {
+		p.discount(ratio)
+	}
+}

interfaces/09-little-refactor/main.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
+
+func main() {
+	l := list{
+		{title: "moby dick", price: 10, released: toTimestamp(118281600)},
+		{title: "odyssey", price: 15, released: toTimestamp("733622400")},
+		{title: "hobbit", price: 25},
+	}
+
+	l.discount(.5)
+	l.print()
+}

interfaces/09-little-refactor/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/09-little-refactor/product.go

@@ -0,0 +1,26 @@
+// 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
+	released timestamp
+}
+
+func (p *product) print() {
+	fmt.Printf("%s: %s (%s)\n", p.title, p.price.string(), p.released.string())
+}
+
+func (p *product) discount(ratio float64) {
+	p.price *= money(1 - ratio)
+}

interfaces/09-little-refactor/timestamp.go

@@ -0,0 +1,45 @@
+// 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"
+)
+
+// timestamp stores, formats and automatically prints a timestamp.
+type timestamp struct {
+	// timestamp anonymously embeds a time.
+	// no need to convert a time value to a timestamp value to use the methods of the time type.
+	time.Time
+}
+
+func (ts timestamp) string() string {
+	if ts.IsZero() { // same as: ts.Time.IsZero()
+		return "unknown"
+	}
+
+	// Mon Jan 2 15:04:05 -0700 MST 2006
+	const layout = "2006/01"
+	return ts.Format(layout) // same as: ts.Time.Format(layout)
+}
+
+// toTimestamp returns a timestamp value depending on the type of `v`.
+func toTimestamp(v interface{}) (ts timestamp) {
+	var t int
+
+	switch v := v.(type) {
+	case int:
+		t = v
+	case string:
+		t, _ = strconv.Atoi(v)
+	}
+
+	ts.Time = time.Unix(int64(t), 0)
+	return ts
+}