How to Use json.RawMessage for Deferred Decoding

Use json.RawMessage to store JSON as a raw byte slice, deferring parsing until you explicitly need the data. This prevents the encoding/json package from unmarshaling the field immediately, saving CPU and memory if the field is never accessed.

import "encoding/json"

type Config struct {
    Name string          `json:"name"`
    Data json.RawMessage `json:"data"` // Deferred decoding
}

func main() {
    var c Config
    json.Unmarshal([]byte(`{"name":"test","data":{"key":"value"}}`), &c)

    // Parse 'Data' only when needed
    var details map[string]interface{}
    json.Unmarshal(c.Data, &details)
}

Think of json.RawMessage as a sealed envelope containing JSON data. Instead of opening and reading the letter immediately, you keep it sealed until you absolutely need the information inside. This saves time and effort if you never actually need to read that specific part of the message.