Returning anonymous type in C#

Question

You can't.

You can only return object, or container of objects, e.g. IEnumerable<object>, IList<object>, etc.

You can return dynamic which will give you a runtime checked version of the anonymous type but only in .NET 4+

In C# 7 we can use tuples to accomplish this:

public List<(int SomeVariable, string AnotherVariable)> TheMethod(SomeParameter)
{
  using (MyDC TheDC = new MyDC())
  {
     var TheQueryFromDB = (....
                       select new { SomeVariable = ....,
                                    AnotherVariable = ....}
                       ).ToList();

      return TheQueryFromDB
                .Select(s => (
                     SomeVariable = s.SomeVariable, 
                     AnotherVariable = s.AnotherVariable))
                 .ToList();
  }
}

You might need to install System.ValueTuple nuget package though.

You cannot return anonymous types. Can you create a model that can be returned? Otherwise, you must use an object.

Here is an article written by Jon Skeet on the subject

Code from the article:

using System;

static class GrottyHacks
{
    internal static T Cast<T>(object target, T example)
    {
        return (T) target;
    }
}

class CheesecakeFactory
{
    static object CreateCheesecake()
    {
        return new { Fruit="Strawberry", Topping="Chocolate" };
    }

    static void Main()
    {
        object weaklyTyped = CreateCheesecake();
        var stronglyTyped = GrottyHacks.Cast(weaklyTyped,
            new { Fruit="", Topping="" });

        Console.WriteLine("Cheesecake: {0} ({1})",
            stronglyTyped.Fruit, stronglyTyped.Topping);            
    }
}

Or, here is another similar article

Or, as others are commenting, you could use dynamic

You can use the Tuple class as a substitute for an anonymous types when returning is necessary:

Note: Tuple can have up to 8 parameters.

return Tuple.Create(variable1, variable2);

Or, for the example from the original post:

public List<Tuple<SomeType, AnotherType>> TheMethod(SomeParameter)
{
  using (MyDC TheDC = new MyDC())
  {
     var TheQueryFromDB = (....
                           select Tuple.Create(..., ...)
                           ).ToList();

      return TheQueryFromDB.ToList();
    }
}

http://msdn.microsoft.com/en-us/library/system.tuple(v=vs.110).aspx

C# compiler is a two phase compiler. In the first phase it just checks namespaces, class hierarchies, Method signatures etc. Method bodies are compiled only during the second phase.

Anonymous types are not determined until the method body is compiled.

So the compiler has no way of determining the return type of the method during the first phase.

That is the reason why anonymous types can not be used as return type.

As others have suggested if you are using .net 4.0 or grater, you can use Dynamic.

If I were you I would probably create a type and return that type from the method. That way it is easy for the future programmers who maintains your code and more readable.