Anonymous class implementing interface

Question

I have the following code inside a method:

 var list = new[]
  {
   new { Name = "Red", IsSelected = true },
   new { Name = "Green", IsSelected = false },
   new { Name = "Blue", IsSelected = false },
  };

I would like to call a function that requires a list of elements with each element implementing an interface (ISelectable). I know how this is done with normal classes, but in this case I am only trying to fill in some demo data.

Is it possible to create an anonymous class implementing an interface?

like this:

new { Name = "Red", IsSelected = true } : ISelectable

score 12 · Accepted Answer · answered Jun 14 '10 at 13:39

No, this is not possible.

An anonymous type is meant to be a lightweight transport object internally. The instant you require more functionality than the little syntax provides, you must implement it as a normal named type.

Things like inheritance and interface implementations, attributes, methods, properties with code, etc. Not possible.

score 12 · Answer 2 · answered Mar 03 '11 at 01:24

12

The open source framework impromptu-interface will allow you to effectively do this with a lightweight proxy and the DLR.

new { Name = "Red", IsSelected = true}.ActLike<ISelectable>();

answered Mar 03 '11 at 01:24

jbtule

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This is amazing! I am playing around with it in LINQPad and it works brilliant so far. – flayn Apr 27 '11 at 21:51

Rodrick Chapman · Answer 3 · 2017-04-27T13:57:50.630

Even if you could do this, you almost certainly would not want to since a method would know everything about the anonymous class (i.e. there is no encapsulation and also no benefit in accessing things indirectly).

On the other hand, I've thought about how such a feature might look (potentially useful if I want to pass an anonymously typed object to a method expecting a particular interface... or so I thought).

The most minimal syntax for an anonymous type that inherits an interface IFoo would be something like

new {IFoo.Bar = 2} // if IFoo.Bar is a property

or

new {IFoo.Bar() = () => do stuff} if IFoo.Bar is a method

But this is the simple case where IFoo only has one property or method. Generally, you would have to implement all of IFoo's members; including read/write properties and events which is currently not even possible on anonymously typed objects.

True, that would be neat. Maybe specify the interface of the anonymous class like this: new {IFoo.Bar = 2}:IFoo; — flayn, Jun 17 '10 at 07:48

Anonymous class implementing interface

3 Answers3