Merging anonymous types

So here's, what I finally came up with (inspired by @BlueMonkMN's answer):

public dynamic Merge(object item1, object item2)
{
    if (item1 == null || item2 == null)
        return item1 ?? item2 ?? new ExpandoObject();

    dynamic expando = new ExpandoObject();
    var result = expando as IDictionary<string, object>;
    foreach (System.Reflection.PropertyInfo fi in item1.GetType().GetProperties())
    {
        result[fi.Name] = fi.GetValue(item1, null);
    }
    foreach (System.Reflection.PropertyInfo fi in item2.GetType().GetProperties())
    {
        result[fi.Name] = fi.GetValue(item2, null);
    }
    return result;
}

You can't, if what you're expecting is a single object where you can access the properties in a compile-time type-safe way (as opposed to a result which is purely dynamic at execution time). The closest you could come would be:

var merged = Tuple.Create(source1, source2);

Console.WriteLine(merged.Item1.foo);
Console.WriteLine(merged.Item1.bar);
Console.WriteLine(merged.Item2.baz);

Bear in mind that anonymous types are created at compile-time. It's not like they're "dynamic" types. You could use ExpandoObject in .NET 4 for that, but it's not quite the same as an anonymous type with all the relevant properties in.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Dynamic;

namespace ConsoleApplication1
{
  class Program
  {
     static void Main(string[] args)
     {
        var source1 = new
        {
            foo = "foo",
            bar = "bar"
        };

        var source2 = new
        {
           baz = "baz"
        };

        dynamic merged = Merge(source1, source2);

        Console.WriteLine("{0} {1} {2}", merged.foo, merged.bar, merged.baz);
     }

     static MergedType<T1, T2> Merge<T1, T2>(T1 t1, T2 t2)
     {
        return new MergedType<T1, T2>(t1, t2);
     }
  }

  class MergedType<T1, T2> : DynamicObject
  {
     T1 t1;
     T2 t2;
     Dictionary<string, object> members = new Dictionary<string, object>(StringComparer.InvariantCultureIgnoreCase);

     public MergedType(T1 t1, T2 t2)
     {
        this.t1 = t1;
        this.t2 = t2;
        foreach (System.Reflection.PropertyInfo fi in typeof(T1).GetProperties())
        {
           members[fi.Name] = fi.GetValue(t1, null);
        }
        foreach (System.Reflection.PropertyInfo fi in typeof(T2).GetProperties())
        {
           members[fi.Name] = fi.GetValue(t2, null);
        }
     }

     public override bool TryGetMember(GetMemberBinder binder, out object result)
     {
        string name = binder.Name.ToLower();
        return members.TryGetValue(name, out result);
     }
  }
}