LINQ .Cast() extension method fails but (type)object works

Question

To convert between some LINQ to SQL objects and DTOs we have created explicit cast operators on the DTOs. That way we can do the following:

DTOType MyDTO =          


        

Answer 1

If you decompile the Linq assembly you get code resembling the following. The previous answer is correct, ultimately the cast is from 'object' to target-type which will always fail for custom types.

private static IEnumerable CastIterator( IEnumerable source )
{
    foreach(object current in source)
    {
        yield return (TResult)( (object)current );
    }
    yield break;
}

public static IEnumerable DCast( this IEnumerable source )
{
    IEnumerable enumerable = source as IEnumerable;
    if(enumerable != null)
    {
        return enumerable;
    }
    if(source == null)
    {
        throw new ArgumentNullException( "source" );
    }
    return CastIterator( source );
}

TFish