Deserialize anonymous type with System.Text.Json

As of .Net 5.0, deserialization of immutable types -- and thus anonymous types -- is supported by System.Text.Json. From How to use immutable types and non-public accessors with System.Text.Json:

System.Text.Json can use a parameterized constructor, which makes it possible to deserialize an immutable class or struct. For a class, if the only constructor is a parameterized one, that constructor will be used.

As anonymous types have exactly one constructor, they can now be deserialized successfully. To do so, define a helper method like so:

public static partial class JsonSerializerExtensions{    public static T DeserializeAnonymousType<T>(string json, T anonymousTypeObject, JsonSerializerOptions options = default)        => JsonSerializer.Deserialize<T>(json, options);    public static ValueTask<TValue> DeserializeAnonymousTypeAsync<TValue>(Stream stream, TValue anonymousTypeObject, JsonSerializerOptions options = default, CancellationToken cancellationToken = default)        => JsonSerializer.DeserializeAsync<TValue>(stream, options, cancellationToken); // Method to deserialize from a stream added for completeness}

And now you can do:

var token = JsonSerializerExtensions.DeserializeAnonymousType(jsonStr, new { token = "" }).token;

Demo fiddle here.

Please try this library I wrote as an extension to System.Text.Json to offer missing features: https://github.com/dahomey-technologies/Dahomey.Json.

You will find support for anonymous types.

Setup json extensions by calling on JsonSerializerOptions the extension method SetupExtensions defined in the namespace Dahomey.Json:

JsonSerializerOptions options = new JsonSerializerOptions();options.SetupExtensions();

Then serialize your class with the JsonSerializerExtensions static type:

var token = JsonSerializerExtensions.DeserializeAnonymousType(jsonStr, new { token = "" }, options).token;