refactor: marshaler unmarshaler iface

interfaces/12-marshaler/main.go

@@ -9,13 +9,45 @@ package main
 
 import (
 	"fmt"
+	"log"
 )
 
 func main() {
-	// removed error handling for brevity (normally you shouldn't do this).
-	out, _ := encode()
-	fmt.Println(string(out))
+	// First encode products as JSON:
+	data, err := encode()
+	if err != nil {
+		log.Fatalln(err)
+	}
+	fmt.Println(string(data))
 
-	l, _ := decode(out)
+	// Then decode them back from JSON:
+	l, err := decode(data)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Let the list value print itself:
 	fmt.Print(l)
 }
+
+/*
+Summary:
+
+- json.Marshal() and json.MarshalIndent() can only encode primitive types.
+  - It cannot encode custom types.
+  - Implement the json.Marshaler interface and teach it how to encode your custom types.
+  - See time.Time code: It satisfies the json.Marshaler interface.
+
+- json.Unmarshal() can only decode primitive types.
+  - It cannot decode custom types.
+  - Implement the json.Unmarshaler interface and teach it how to decode your custom types.
+  - See time.Time code: It satisfies the json.Unmarshaler interface as well.
+
+- strconv.AppendInt() can append an int value to a []byte.
+  - There are several other functions in the strconv package for other primitive types as well.
+  - Do not make unnecessary string <-> []byte conversions.
+
+- log.Fatalln() can print the given error message and terminate the program.
+  - Use it only from the main(). Do not use it in other functions.
+  - main() is should be the main driver of a program.
+*/