using System;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        const string json = @"{""MyInt"":123,""MyBool"":true,""MyString"":""Hello""}";

​

        var obj = JsonSerializer.Deserialize<ClassWithPrimitives>(json);

        Console.WriteLine(123 == obj.MyInt);

        Console.WriteLine(obj.MyBool);

        Console.WriteLine("Hello" == obj.MyString);

    }

    private class ClassWithPrimitives

    {

        [JsonConverter(typeof(PrimitiveConverter))]

        public int MyInt { get; set; }

        [JsonConverter(typeof(PrimitiveConverter))]

        public bool MyBool { get; set; }

        [JsonConverter(typeof(PrimitiveConverter))]

        public string MyString { get; set; }

    }

    private class PrimitiveConverter : JsonConverter<object>

    {

        public override object Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

        {

            if (reader.TokenType == JsonTokenType.True)

            {

                return true;

            }

​

            if (reader.TokenType == JsonTokenType.False)

            {

                return false;

            }

​

            if (reader.TokenType == JsonTokenType.Number)

            {

                if (reader.TryGetInt32(out int i))

                {

                    return i;

                }

​

                return reader.GetDouble();

            }

​

            if (reader.TokenType == JsonTokenType.String)

            {

                if (reader.TryGetDateTime(out DateTime datetime))

                {

                    return datetime;

                }

​

                return reader.GetString();

            }

​

            throw new JsonException();

        }

​

        public override void Write(Utf8JsonWriter writer, object value, JsonSerializerOptions options)

        {

            throw new InvalidOperationException("Should not get here.");

        }

    }

}