Source generation: size

Size.cs

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace Size
{
    class Program
    {
        static void Main(string[] args)
        {
            Message obj = new() { Data = "Hello", "World" };

            // Size-optimal implementation.
            byte[] json = JsonSerializer.SerializeToUtf8Bytes(obj, JsonContext.Default.MyClass);
            obj = JsonSerializer.Deserialize(json, JsonContext.Default.MyClass);

            // Alternate implementation.
            // byte[] json = JsonSerializer.SerializeToUtf8Bytes(obj);
            // obj = JsonSerializer.Deserialize(json);
        }
    }

    public struct Message
    {
        public string Data { get; set; }
    }

    [JsonSerializable(typeof(Message))]
    internal class MyJsonContext
    {
    }
}