How to Use the encoding.TextMarshaler and encoding.TextUnmarshaler Interfaces

Implement MarshalText() to convert your type to a byte slice and UnmarshalText() to parse a byte slice back into your type. The encoding/json package automatically uses these methods when marshaling or unmarshaling your type.

type MyType struct {
    Value int
}

func (m MyType) MarshalText() ([]byte, error) {
    return []byte(fmt.Sprintf("%d", m.Value)), nil
}

func (m *MyType) UnmarshalText(text []byte) error {
    n, err := strconv.Atoi(string(text))
    if err != nil {
        return err
    }
    m.Value = n
    return nil
}

These interfaces let your custom data types define their own text format for saving and loading. When you save data to JSON, Go calls your MarshalText function to turn your object into a string. When you load data from JSON, Go calls your UnmarshalText function to turn that string back into your object. It's like giving your data type a custom translator for text-based formats.