refactor: common ifaces

interfaces/11-sort/list.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 (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// product is now *product because sorting will unnecessarily copy the product values
+
+type list []*product
+
+func (l list) String() string {
+	if len(l) == 0 {
+		return "Sorry. We're waiting for delivery 🚚.\n"
+	}
+
+	sort.Sort(l)
+	var str strings.Builder
+	for _, p := range l {
+		fmt.Fprintf(&str, "* %s\n", p)
+	}
+	return str.String()
+}
+
+func (l list) discount(ratio float64) {
+	for _, p := range l {
+		p.discount(ratio)
+	}
+}
+
+// by default `list` sorts by `title`.
+func (l list) Len() int           { return len(l) }
+func (l list) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
+func (l list) Less(i, j int) bool { return l[i].title < l[j].title }
+
+// byRelease sorts by product release dates.
+type byRelease struct {
+	// byRelease embeds `list` and reuses list's Len and Swap methods.
+	list
+}
+
+func (bp byRelease) Less(i, j int) bool {
+	// Before() accepts a time.Time but `released` is not time.Time.
+	// `released.Time` is necessary.
+	return bp.list[i].released.Before(bp.list[j].released.Time)
+}

interfaces/11-sort/main.go

@@ -0,0 +1,28 @@
+// 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"
+	"sort"
+)
+
+func main() {
+	l := list{
+		{title: "moby dick", price: 10, released: toTimestamp(118281600)},
+		{title: "odyssey", price: 15, released: toTimestamp("733622400")},
+		{title: "hobbit", price: 25},
+	}
+
+	// sort.Sort(l)
+	// sort.Sort(sort.Reverse(l))
+	// sort.Sort(byRelease{l})
+	sort.Sort(sort.Reverse(byRelease{l}))
+
+	fmt.Print(l)
+}

interfaces/11-sort/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/11-sort/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) String() string {
+	return fmt.Sprintf("%s: %s (%s)", p.title, p.price, p.released)
+}
+
+func (p *product) discount(ratio float64) {
+	p.price *= money(1 - ratio)
+}

interfaces/11-sort/timestamp.go

@@ -0,0 +1,41 @@
+// 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"
+)
+
+type timestamp struct {
+	time.Time
+}
+
+func (ts timestamp) String() string {
+	if ts.IsZero() {
+		return "unknown"
+	}
+
+	// Mon Jan 2 15:04:05 -0700 MST 2006
+	const layout = "2006/01"
+	return ts.Format(layout)
+}
+
+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
+}