refactor: common ifaces

interfaces/12-marshaler/list.go

@@ -0,0 +1,49 @@
+// 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"
+)
+
+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 {
+	list
+}
+
+func (bp byRelease) Less(i, j int) bool {
+	return bp.list[i].Released.Before(bp.list[j].Released.Time)
+}