Explain how encoding/json marshaling works with struct tags and custom marshalers.

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Accepted Answer

type User struct {
    ID        string    `json:"id"`
    Name      string    `json:"name"`
    Email     string    `json:"email,omitempty"` // omit if empty
    Password  string    `json:"-"`               // never serialize
    CreatedAt time.Time `json:"created_at"`
}

// Custom marshaler example — serialize sensitive fields differently
type Money struct {
    Amount   int64  // stored in cents
    Currency string
}

func (m Money) MarshalJSON() ([]byte, error) {
    return json.Marshal(struct {
        Amount   float64 `json:"amount"`
        Currency string  `json:"currency"`
    }{
        Amount:   float64(m.Amount) / 100.0,
        Currency: m.Currency,
    })
}

func (m *Money) UnmarshalJSON(data []byte) error {
    var v struct {
        Amount   float64 `json:"amount"`
        Currency string  `json:"currency"`
    }
    if err := json.Unmarshal(data, &v); err != nil {
        return err
    }
    m.Amount = int64(v.Amount * 100)
    m.Currency = v.Currency
    return nil
}

// Decoding numbers safely from interface{}
dec := json.NewDecoder(r.Body)
dec.UseNumber() // numbers remain json.Number, not float64
var data map[string]interface{}
dec.Decode(&data) Unexported fields are silently ignored — always export fields you want serialized interface{} numbers unmarshal as float64 by default — use UseNumber() for large integers omitempty omits zero values: 0, false, "", nil — careful with intentional zero values Anonymous embedded structs promote their fields to the parent — useful but can cause field collisions json.RawMessage allows deferring or passing through raw JSON without parsing

Explain how encoding/json marshaling works with struct tags and custom marshalers.

encoding/json uses struct tags to control JSON field names and behavior. Implement json.Marshaler and json.Unmarshaler interfaces for custom serialization logic.

Explain how encoding/json marshaling works with struct tags and custom marshalers.

encoding/json uses struct tags to control JSON field names and behavior. Implement json.Marshaler and json.Unmarshaler interfaces for custom serialization logic.

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