How to Serialize a Mixed-Type JSON Array in Go?

Serialize a Mixed Type JSON Array in Go

In Go, serializing a heterogenous array of strings, floating point numbers, and unicode characters into a JSON array might seem challenging due to the lack of built-in support for mixed type arrays. However, by implementing the json.Marshaler interface, we can customize how objects are serialized to achieve this.

Implementing the MarshalJSON Method

To serialize a structure like Row as an array of arrays, we create a MarshalJSON method on the Row type. This method converts the Row struct into an array of generic interface values and then serializes them using json.Marshal:

func (r *Row) MarshalJSON() ([]byte, error) {
    arr := []interface{}{r.Ooid, r.Score, r.Text}
    return json.Marshal(arr)
}

Example Usage

With the MarshalJSON method in place, we can serialize a slice of Row elements into a valid JSON array:

rows := []Row{{"ooid1", 2.0, "Söme text"}, {"ooid2", 1.3, "Åther text"}}
marshalled, _ := json.Marshal(rows)

// Output:
// {"results": [["ooid1", 2.0, "Söme text"], ["ooid2", 1.3, "Åther text"]]}

Unmarshaling from JSON

If needed, we can also implement the json.Unmarshaler interface to deserialize JSON data back into Row structs. This involves a similar approach of using an intermediate slice of interface values to store the values extracted from the JSON array:

func (r *Row) UnmarshalJSON(bs []byte) error {
    arr := []interface{}{}
    json.Unmarshal(bs, &arr)
    // TODO: add error handling here.
    r.Ooid = arr[0].(string)
    r.Score = arr[1].(float64)
    r.Text = arr[2].(string)
    return nil
}

By implementing the json.Marshaler and json.Unmarshaler interfaces, we can effectively serialize and deserialize mixed type arrays in Go, enabling us to manipulate data structures with heterogenous elements as JSON.

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