Why does interface assertion fail during JSON deserialization?

Interface Assertion Fails During JSON Deserialization

When attempting to assert an interface to a specific struct type after deserializing from JSON, an error occurs:

panic: interface conversion: interface {} is map[string]interface {},
not main.Data

This issue arises because the assertion is being made to an incompatible type. An interface can only be converted to a specific type if it was originally assigned a value of that type.

In the provided code, the interface anInterface is assigned the value of the Data struct AData. Therefore, anInterface can safely be asserted to Data.

type Data struct {
    Content string
    Links   []string
}

func main() {
    var AData, AData2 Data
    var anInterface interface{}

    // populate data
    AData.Content = "hello world"
    AData.Links = []string{"link1", "link2", "link3"}
    anInterface = AData
    AData2 = anInterface.(Data)
}

Conversely, if the interface anInterface were assigned a value of type map[string]interface{}, it could not be asserted to Data.

To directly deserialize JSON data into a Data struct, use the json.Unmarshal() function.

var AData2 Data

err = json.Unmarshal([]byte(value), &AData2)
if err != nil {
    panic(err)
}

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