add: reflection decoder

interfaces/11-reflection-decoder/decoder.go

@@ -0,0 +1,63 @@
+// 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"
+
+type decoderSchema struct {
+	Category string
+
+	// json.RawMessage is a special type of the json package.
+	// It prevents the json package functions encode/decode
+	// the specific parts of the json data.
+	Item json.RawMessage
+}
+
+func decode(data []byte) (list, error) {
+	var schemas []decoderSchema
+
+	if err := json.Unmarshal(data, &schemas); err != nil {
+		return nil, err
+	}
+
+	return toStore(schemas)
+}
+
+func toStore(schemas []decoderSchema) (store list, err error) {
+	for _, s := range schemas {
+		p := newProduct(s.Category)
+
+		if json.Unmarshal(s.Item, &p); err != nil {
+			return nil, err
+		}
+
+		store = append(store, p)
+	}
+	return store, nil
+}
+
+func newProduct(category string) item {
+	// for each product you need to open this code
+	// and add a new case.
+	//
+	// dependency injection should be the responsibility
+	// of the user of this function.
+	switch category {
+	case "book":
+		// var b book
+		// return &b
+		return new(book)
+	case "game":
+		return new(game)
+	case "puzzle":
+		return new(puzzle)
+	case "toy":
+		return new(toy)
+	}
+	return nil
+}