Here are a few title options, focusing on the problem and solution: **Direct Question

JSON Decoding into Structs vs. Maps

In the scenario described, an application receives an interface{} containing a struct that matches the JSON structure received as a byte array. However, upon JSON decoding, the result is a map instead of the expected struct.

This behavior is due to the way json.Unmarshal handles pointers. By referencing an interface{} that originally held the struct, the decoding process is unable to determine the underlying type. As a result, it returns a simple map instead of the desired struct.

To rectify this issue, two approaches can be considered:

1. Direct Interface Casting:

Pass a pointer to the struct directly to json.Unmarshal as an abstract interface:

<code class="go">var ping interface{} = &Ping{}
deserialize([]byte(`{"id":42}`), ping)</code>

2. Reflection-Based Pointer Creation:

If a direct pointer to the struct is unavailable, utilize reflection to create a new pointer, deserialize into it, and copy the value back:

<code class="go">var ping interface{} = Ping{}
nptr := reflect.New(reflect.TypeOf(ping))
deserialize([]byte(`{"id":42}`), nptr.Interface())
ping = nptr.Interface()</code>

By adopting either of these approaches, the decoding process can correctly identify the underlying struct and populate its fields from the JSON data.

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