How to implement custom encoding and decoding methods for user-defined types in Go?

To implement custom encoding and decoding methods for user-defined types in Go, you can make use of the encoding package in the Go standard library. Here's a step-by-step guide on how to do that:

Step 1: Define your user-defined type First, define your user-defined type with the required fields and methods. Let's say we have a Person struct with a Name field:

type Person struct {
    Name string
}

Step 2: Implement the MarshalJSON method Next, implement the MarshalJSON method for your user-defined type. This method should return a byte array representing the JSON-encoded form of your object. In our case, it would look like this:

func (p *Person) MarshalJSON() ([]byte, error) {
    return []byte("\"" + p.Name + "\""), nil
}

Step 3: Implement the UnmarshalJSON method Similarly, implement the UnmarshalJSON method for your user-defined type. This method should take a byte array as input and fill the fields of your object based on the JSON representation. In our case, it would be:

func (p *Person) UnmarshalJSON(data []byte) error {
    var name string
    err := json.Unmarshal(data, &name)
    if err != nil {
        return err
    }
    p.Name = name[1 : len(name)-1]
    return nil
}

Note that we are using the encoding/json package to simplify JSON encoding and decoding operations.

Step 4: Test the encoding and decoding methods Create a test function to verify your encoding and decoding methods:

func main() {
    p1 := &Person{Name: "John"}
    jsonBytes, _ := json.Marshal(p1)
    fmt.Println(string(jsonBytes)) // Output: "John"
    
    var p2 Person
    json.Unmarshal(jsonBytes, &p2)
    fmt.Println(p2.Name) // Output: John
}

In this example, we create a Person object p1, marshal it into JSON using json.Marshal, and verify that the JSON representation is "John". Then, we unmarshal the JSON back into a Person object p2 using json.Unmarshal and verify that the Name field is properly set.

That's it! By implementing the MarshalJSON and UnmarshalJSON methods for your user-defined type, you can define how it should be encoded and decoded in JSON format.