## Why does `json.Unmarshal` return a map instead of a struct when unmarshaling into an interface{}?

Anomalous Return Type from Marshaling Interface with JSON

In scenarios where json.Unmarshal is employed to converta byte array into an interface{}, an unexpected result may arise where a map is returned instead of the anticipated struct type. This discrepancy can be attributed to the abstract nature of the interface{} type, leaving the json package unable to discern the underlying struct structure.

To rectify this anomaly, it is recommended to explicitly pass a pointer to the desired struct, casting it as an abstract interface. This approach allows the json package to recognize and deserialize the struct accordingly.

For instance, the following modified code snippet illustrates the desired behavior:

<code class="go">func bad() {
    var ping interface{} = &Ping{} // Pass a pointer to Ping as an interface
    deserialize([]byte(`{"id":42}`), ping)
    fmt.Println("DONE:", ping) // Now outputs a Ping struct
}</code>

Alternatively, if access to a pointer is not feasible, dynamic allocation can be utilized to create a new pointer that can be deserialized. The original interface{} value can then be updated with the new value.

<code class="go">func bad() {
    var ping interface{} = Ping{}
    nptr := reflect.New(reflect.TypeOf(ping))
    deserialize([]byte(`{"id":42}`), nptr.Interface())
    ping = nptr.Interface()
    fmt.Println("DONE:", ping) // Outputs a Ping struct
}</code>

By employing one of these techniques, the json.Unmarshal function can accurately deserialize the byte array into the desired struct type, eliminating the unexpected map return value.

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