using System;
using System.Linq;
using System.Collections.Generic;
 
public class Program
{
    public interface ITaggable {}
 
    public struct TagStruct : ITaggable {}
    public class  TagObject : ITaggable {}
 
    public static IEnumerable<T> DoSomething<T>(IEnumerable<T> input) 
        where T: ITaggable
    {
        foreach (var i in input) yield return i;
    }
 
    public static void Main(string[] args)
    {
        var structs = new [] { new TagStruct() };
        var objects = new [] { new TagObject() };
 
        Console.WriteLine(DoSomething(structs).First().GetType());
        Console.WriteLine(DoSomething(objects).First().GetType());
 
 
 
    }
}
 

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