using System;
using System.Linq;
using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Reflection;
using System.Linq.Expressions;
using System.Threading;
using System.Threading.Tasks;

var data = CustomAttributeData.GetCustomAttributes(typeof(Annotated)).Single(item => item.AttributeType == typeof(MarkerAttribute));
Console.WriteLine($"data:{data.ConstructorArguments[0].Value}");
Console.WriteLine($"constructors:{MarkerAttribute.Created}");
var instance = (MarkerAttribute)Attribute.GetCustomAttribute(typeof(Annotated), typeof(MarkerAttribute))!;
Console.WriteLine($"instance:{instance.Name}");
Console.WriteLine($"constructors:{MarkerAttribute.Created}");
[Marker("demo")] sealed class Annotated { }
[AttributeUsage(AttributeTargets.Class)]
sealed class MarkerAttribute : Attribute
{
    public static int Created;
    public string Name { get; }
    public MarkerAttribute(string name) { Name = name; Created++; }
}