title: map to derived type of destination in AutoMapper
body: <p>I want to specify a mapping so that all mappings from "Source" to "Destination" is returned as a derived class of "Destination"</p>
  
  <pre><code>    [Test]
      public void Map_SourceToDestinationAsDerivedType_ReturnsDerivedType()
      {
          // arrange
          AutoMapper.Mapper.CreateMap&lt;Source, Destination&gt;()
              .CreateAs&lt;ActualDestination&gt;() // psedu code
              .ForMember(dst =&gt; dst.Transformed, opt =&gt; opt.ResolveUsing(src =&gt; src.Property));
  
          var source = new Source{Property = "hi mom" };
  
          // act
          var destination = AutoMapper.Mapper.Map&lt;Destination&gt;(source);
  
          // assert
          Assert.That(destination, Is.InstanceOf&lt;ActualDestination&gt;());
      }
  
      public class Source
      {
          public string Property { get; set; }
      }
  
      public class Destination
      {
  
      }
  
      public class ActualDestination : Destination
      {
          public string Transformed { get; set; }            
      }
  </code></pre>