add: type switch

interfaces/06-empty-interface/book.go

@@ -0,0 +1,47 @@
+// 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"
+	"strconv"
+	"time"
+)
+
+type book struct {
+	title     string
+	price     money
+	published interface{}
+}
+
+func (b book) print() {
+	p := format(b.published)
+	fmt.Printf("%-15s: %s - (%v)\n", b.title, b.price.string(), p)
+}
+
+func format(v interface{}) string {
+	// book{title: "hobbit", price: 25},
+	if v == nil {
+		return "unknown"
+	}
+
+	var t int
+
+	// book{title: "moby dick", price: 10, published: 118281600},
+	if v, ok := v.(int); ok {
+		t = v
+	}
+
+	// book{title: "odyssey", price: 15, published: "733622400"},
+	if v, ok := v.(string); ok {
+		t, _ = strconv.Atoi(v)
+	}
+
+	u := time.Unix(int64(t), 0)
+	return u.String()
+}