Develop Reference

Generic Extension Method with Concrete Class Override

I have a third party DLL that returns objects like Customers, Orders, etc. I'll call them Your Entities. They do have a common IYourEntity interface so I can use that as a source constraint.
I want to create a generic conversion extension method to convert all these different third party entities to My Entities with some streamlined and more maintainable code.
....but I can't figure out how to make a generic extension method that will call the concrete extension method for the specific conversion of each class.
Putting some of the main aspects of my code below, but you can get a full fiddle to play with here.
Yes, I'm probably showing I'm a bit clueless on how to do this and maybe trying to combine different concepts. Any pointers much appreciated as I've been beating my head for a couple of days now and need a life line :)
public interface IYourEntity
{
int Id
{
get;
set;
}
}
public interface IConvertToMyEntity<TYourEntity, TMyEntity>
where TYourEntity : class, IYourEntity, new()
where TMyEntity : class, IMyEntity, new()
{
TMyEntity ToMyEntity(TYourEntity yourEntity);
}
public static class ExtensionMethods
{
private static IMyEntity ToMyEntity(this IYourEntity yourEntity)
{
return new MyEntity1();
}
public static List<IMyEntity> ToMyEntityList(this List<IYourEntity> lstYourEntities)
{
return lstYourEntities.ConvertAll(q => q.ToMyEntity());
}
}
public class YourEntity1 : IYourEntity, IConvertToMyEntity<YourEntity1, MyEntity1>
{
public int Id
{
get;
set;
}
public string YourEntityName
{
get;
set;
}
public MyEntity1 ToMyEntity(YourEntity1 yourEntity)
{
return new MyEntity1()
{Id = yourEntity.Id, MyEntityName = yourEntity.YourEntityName, CreatedOn = DateTime.UtcNow};
}
public List<MyEntity1> ToMyEntityList(List<YourEntity1> lstYourEntities)
{
return lstYourEntities.ConvertAll(q => ToMyEntity(q));
}
}

Since the classes implementing IYourEntity are from a third party and not under your control, you can't implement an own IConvertToMyEntity<T1, T2> interface upon these.
One way you can handle it is by overloads of such conversion (extension) methods.
There's no need for any generic T type arguments; the common IYourEntity interface suffices.
Suppose you have 3 classes implementing the IYourEntity interface;
e.g. YourCustomer, YourOrder and YourProduct.
These need to be converted to IMyEntity instances, of which you might have different concrete implementations;
e.g. a general MyEntity and a specific MyProduct.
For the conversion you set up an extension method targeting IYourEntity.
This extension method will be called to convert an IYourEntity to an IMyEntity in case a more specific overload of this extension method does not exist.
public static IMyEntity ToMyEntity(this IYourEntity target)
{
return new MyEntity { Id = target.Id, EntityName = "Fallback name" };
}
For the entities that require a custom conversion, you set up overloads of this extension method targeting those specific source class types.
Below are such ones for YourOrder and YourProduct (but not for YourCustomer).
public static IMyEntity ToMyEntity(this YourOrder target)
{
return new MyEntity { Id = target.Id, EntityName = target.OrderName.ToUpper() };
}
public static IMyEntity ToMyEntity(this YourProduct target)
{
return new MyProduct { Id = target.Id * 100, EntityName = target.ProductName };
}
Next, define the extension method to convert the list of IYourEntity instances to a list of IMyEntity instances. In the code below, the inbetween cast to dynamic enables that the appropriate ToMyEntity overload will be called.
Note that the ToMyEntity methods don't have to be extension methods, but it might be convenient to have these in place in case you need to convert a single instance instead of a list.
public static List<IMyEntity> ToMyEntities(this List<IYourEntity> target)
{
var myEntities = new List<IMyEntity>();
foreach (var yourEntity in target)
{
var myEntity = Extensions.ToMyEntity((dynamic)yourEntity);
myEntities.Add(myEntity);
}
return myEntities;
}
An example - .net fiddle
var yourEntities = new List<IYourEntity>()
{
new YourCustomer() { Id = 1 },
new YourOrder() { Id = 2, OrderName = "Order-2"},
new YourProduct() { Id = 3, ProductName = "Product-3"}
};
var myEnties = yourEntities.ToMyEntities();
myEnties.ForEach(o => Console.WriteLine("{0} - {1} ({2})",
o.Id, o.EntityName, o.GetType().Name
));
The output of the example above looks like below.
Notice how the YourCustomer instance was handled by the general IYourEntity conversion, whereas the YourOrder and YourProduct instances got a specific treatment.
1 - Fallback name (MyEntity)
2 - ORDER-2 (MyEntity)
300 - Product-3 (MyProduct)

You can change your extension method to this:
private static IMyEntity ToMyEntity(this IYourEntity yourEntity)
{
if (yourEntity is IConvertToMyEntity<IYourEntity, IMyEntity> convertible)
return convertible.ToMyEntity;
return new MyEntity1();
}
This will not work in most cases unless you also make your interface co- and contra-variant:
public interface IConvertToMyEntity<in TYourEntity, out TMyEntity>
where TYourEntity : class, IYourEntity, new()
where TMyEntity : class, IMyEntity, new()
{
TMyEntity ToMyEntity(TYourEntity yourEntity);
}

It is still not completely clear to me how you can make a third party class implements IConvertToMyEntity that easily. Assuming you did this only to show us your actual goal, you should be very careful with what you are trying to accomplish in the Main.
If you use a List<IYourEntity>, you can only use methods and properties defined in the interface, unless you know what you are doing with specific cast. The need for List<IYourEntity> or List<IMyEntity> limits a lot the implementation of a custom mapper between My classes and Your classes. Here a possible solution:
As I said, I did not change Your classes:
public interface IYourEntity
{
int Id
{
get;
set;
}
}
public class YourEntity1 : IYourEntity
{
public int Id
{
get;
set;
}
public string YourEntityName
{
get;
set;
}
}
Also My classes are very simple and do not contain any logic for the mapping. This is a debatable choice, but I generally prefer to keep conversion logic separated from the classes involved. This helps to maintain clean your code in case you have several conversion functions for the same pair of classes. By the way, here they are:
public interface IMyEntity
{
int Id
{
get;
set;
}
DateTime CreatedOn
{
get;
set;
}
}
public class MyEntity1 : IMyEntity
{
public int Id
{
get;
set;
}
public string MyEntityName
{
get;
set;
}
public DateTime CreatedOn
{
get;
set;
}
}
And this is how I designed the custom converter
public interface IMyEntityConverter
{
IMyEntity Convert(IYourEntity yourEntity);
}
public class MyEntity1Converter : IMyEntityConverter
{
public IMyEntity Convert(IYourEntity yourEntity)
{
var castedYourEntity = yourEntity as YourEntity1;
return new MyEntity1()
{
Id = castedYourEntity.Id,
MyEntityName = castedYourEntity.YourEntityName,
CreatedOn = DateTime.UtcNow
};
}
}
It is clear the lack of genericity, but you cannot do otherwise if you need an extension method on a List of generic My and Your classes. Also tried with covariant and contravariant interfaces but C# does not let you use them with this implementation.
Now the core of the solution: you need something that binds Your class to the My class with a custom converter, and all of this should be as more transparent as possible.
public class EntityAdapter<YourType, MyType>
where YourType : IYourEntity
where MyType : IMyEntity
{
protected YourType wrappedEntity;
protected IMyEntityConverter converter;
public EntityAdapter(YourType wrappedEntity, IMyEntityConverter converter)
{
this.wrappedEntity = wrappedEntity;
this.converter = converter;
}
public static implicit operator YourType(EntityAdapter<YourType, MyType> entityAdapter) => entityAdapter.wrappedEntity;
public static explicit operator MyType(EntityAdapter<YourType, MyType> entityAdapter) =>
(MyType) entityAdapter.converter.Convert(entityAdapter.wrappedEntity);
public MyType CastToMyEntityType()
{
return (MyType) this;
}
}
The pseudo-transparency here is given by the implicit cast to Your class. The advantage is that you can cast this EntityAdapter to an instance of a My class by calling CastToMyEntityType or the explicit operator overload.
The painful part is with the extension methods:
public static class EntityAdapterExtensions
{
public static List<IMyEntity> ToIMyEntityList(this List<EntityAdapter<IYourEntity, IMyEntity>> lstEntityAdapters)
{
return lstEntityAdapters.ConvertAll(e => e.CastToMyEntityType());
}
public static List<EntityAdapter<IYourEntity, IMyEntity>> ToEntityAdapterList(this List<IYourEntity> lstYourEntities)
{
return lstYourEntities.Select(e =>
{
switch (e)
{
case YourEntity1 yourEntity1:
return new EntityAdapter<IYourEntity, IMyEntity>(yourEntity1, new MyEntity1Converter());
default:
throw new NotSupportedException("You forgot to map " + e.GetType());
}
}).ToList();
}
}
The first one is pretty straightforward to understand, but the second one is definitely something that require maintenance. I gave up on generics for the reasons already explained, so the only thing left to do is to create the EntityAdapters starting from the actual entity types.
Here is the fiddle

This may be a little controversial but maybe a different way is better?
Firstly, and this is more for my sake, I would suggest more easily understandable terminology so instead of 'your' and 'my' I would use 'source' and 'dest'.
Secondly I wonder if the generics route is necessary? I'm assuming (and I may be wrong) that for each of the classes you have coming from your third-party assembly, you have a specific class for it to be converted to. So maybe this could be achieved much more easily with a constructor override in your destination class.
// third party class example
public class SourceClass
{
public int Id { get; set; }
public string Name { get; set; }
}
// the destination class in your project
public class DestClass
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime CreatedOn { get; set; }
// default constructor
public DestClass()
{
}
// conversion constructor
public DestClass(SourceClass source)
{
Id = source.Id;
Name = source.Name;
CreatedOn = DateTime.UtcNow;
}
}
This way you convert a single instance using:
// source being an instance of the third-party class
DestClass myInstance = new DestClass(source);
And you can convert a list with LINQ:
// source list is IList<SourceClass>
IList<DestClass> myList = sourceList.Select(s => new DestClass(s)).ToList();
If you wanted to you could implement extensions for your conversions. This again would not be generic as you'll need one for each class pairing but as it's an alternative to writing a converter class for each, it will be overall less code.
public static class SourceClassExtensions
{
public static DestClass ToDest(this SourceClass source)
=> new DestClass(source);
public static IList<DestClass> ToDest(this IList<SourceClass> source)
=> source.Select(s => new DestClass(s)).ToList();
}
If you still want something generic then you'll want a converter for each class pair, implementing a suitable interface. Then I'd recommend a converter factory class where you'll need to register the specific converters either into a dictionary in the class or via dependency injection. I can go into this further if you'd prefer but I think it would be more complicated.

sorry for writing here its not an actual answer,
there is no option for generically to do this
you have to write for every entity
public interface IConvertToMyEntity<TYourEntity, TMyEntity>
where TYourEntity : class, IYourEntity, new()
where TMyEntity : class, IMyEntity, new()
{
TMyEntity ToMyEntity(TYourEntity yourEntity);
}
I saw this code from your question.
It depends on what you want to do after transformation
you should use data mapper
public class MapProfile : Profile
{
public MapProfile()
{
CreateMap<TYourEntity , TMyEntity >();
CreateMap<TMyEntity , TYourEntity >();
}
}

List of unknown generic types or invoke a generic subclass [duplicate]

Is it possible to add different type of generic objects to a list?. As below.
public class ValuePair<T>
{
public string Name { get; set;}
public T Value { get; set;
}
and let say I have all these objects...
ValuePair<string> data1 = new ValuePair<string>();
ValuePair<double> data2 = new ValuePair<double>();
ValuePair<int> data3 = new ValuePair<int>();
I would like to hold these objects in a generic list.such as
List<ValuePair> list = new List<ValuePair>();
list.Add(data1);
list.Add(data2);
list.Add(data3);
Is it possible?

In general, you'd have to either use a List<object> or create a non-generic base class, e.g.
public abstract class ValuePair
{
public string Name { get; set;}
public abstract object RawValue { get; }
}
public class ValuePair<T> : ValuePair
{
public T Value { get; set; }
public object RawValue { get { return Value; } }
}
Then you can have a List<ValuePair>.
Now, there is one exception to this: covariant/contravariant types in C# 4. For example, you can write:
var streamSequenceList = new List<IEnumerable<Stream>>();
IEnumerable<MemoryStream> memoryStreams = null; // For simplicity
IEnumerable<NetworkStream> networkStreams = null; // For simplicity
IEnumerable<Stream> streams = null; // For simplicity
streamSequenceList.Add(memoryStreams);
streamSequenceList.Add(networkStreams);
streamSequenceList.Add(streams);
This isn't applicable in your case because:
You're using a generic class, not an interface
You couldn't change it into a generic covariant interface because you've got T going "in" and "out" of the API
You're using value types as type arguments, and those don't work with generic variable (so an IEnumerable<int> isn't an IEnumerable<object>)

Not unless you have a non-generic base-type ValuePair with ValuePair<T> : ValuePair (it would work for an interface too), or use List<object>. Actually, though, this works reasonably:
public abstract class ValuePair
{
public string Name { get; set; }
public object Value
{
get { return GetValue(); }
set { SetValue(value); }
}
protected abstract object GetValue();
protected abstract void SetValue(object value);
}
public class ValuePair<T> : ValuePair
{
protected override object GetValue() { return Value; }
protected override void SetValue(object value) { Value = (T)value; }
public new T Value { get; set; }
}

No, it is not possible. You could create, in your case, a base class ValuePair from which ValuePair<T> derives. Depends on your purposes.

it's not possible as far as I know.
the line:
List<ValuePair> list = new List<ValuePair>();
you wrote in your sample is not providing a concrete type for T and this is the issue, once you pass it, you can only add object of that specific type.

Adding different type of generic objects into generic list

Is it possible to add different type of generic objects to a list?. As below.
public class ValuePair<T>
{
public string Name { get; set;}
public T Value { get; set;
}
and let say I have all these objects...
ValuePair<string> data1 = new ValuePair<string>();
ValuePair<double> data2 = new ValuePair<double>();
ValuePair<int> data3 = new ValuePair<int>();
I would like to hold these objects in a generic list.such as
List<ValuePair> list = new List<ValuePair>();
list.Add(data1);
list.Add(data2);
list.Add(data3);
Is it possible?

In general, you'd have to either use a List<object> or create a non-generic base class, e.g.
public abstract class ValuePair
{
public string Name { get; set;}
public abstract object RawValue { get; }
}
public class ValuePair<T> : ValuePair
{
public T Value { get; set; }
public object RawValue { get { return Value; } }
}
Then you can have a List<ValuePair>.
Now, there is one exception to this: covariant/contravariant types in C# 4. For example, you can write:
var streamSequenceList = new List<IEnumerable<Stream>>();
IEnumerable<MemoryStream> memoryStreams = null; // For simplicity
IEnumerable<NetworkStream> networkStreams = null; // For simplicity
IEnumerable<Stream> streams = null; // For simplicity
streamSequenceList.Add(memoryStreams);
streamSequenceList.Add(networkStreams);
streamSequenceList.Add(streams);
This isn't applicable in your case because:
You're using a generic class, not an interface
You couldn't change it into a generic covariant interface because you've got T going "in" and "out" of the API
You're using value types as type arguments, and those don't work with generic variable (so an IEnumerable<int> isn't an IEnumerable<object>)

Not unless you have a non-generic base-type ValuePair with ValuePair<T> : ValuePair (it would work for an interface too), or use List<object>. Actually, though, this works reasonably:
public abstract class ValuePair
{
public string Name { get; set; }
public object Value
{
get { return GetValue(); }
set { SetValue(value); }
}
protected abstract object GetValue();
protected abstract void SetValue(object value);
}
public class ValuePair<T> : ValuePair
{
protected override object GetValue() { return Value; }
protected override void SetValue(object value) { Value = (T)value; }
public new T Value { get; set; }
}

No, it is not possible. You could create, in your case, a base class ValuePair from which ValuePair<T> derives. Depends on your purposes.

it's not possible as far as I know.
the line:
List<ValuePair> list = new List<ValuePair>();
you wrote in your sample is not providing a concrete type for T and this is the issue, once you pass it, you can only add object of that specific type.

C# class design with Generic structure

This might be a simple one, but my head is refusing to wrap around that, so an outside view is always useful in that case!
I need to design an object hierarchy to implement a Parameter Registration for a patient. This will take place on a certain date and collect a number of different parameters about a patient (bloodpressure, heartrate etc). The values of those Parameter Registrations can be of different types, such as strings, integers, floats or even guids (for lookup lists).
So we have:
public class ParameterRegistration
{
public DateTime RegistrationDate { get; set; }
public IList<ParameterRegistrationValue> ParameterRegistrationValues { get; set; }
}
public class ParameterRegistrationValue
{
public Parameter Parameter { get; set; }
public RegistrationValue RegistrationValue { get; set; } // this needs to accomodate the different possible types of registrations!
}
public class Parameter
{
// some general information about Parameters
}
public class RegistrationValue<T>
{
public RegistrationValue(T value)
{
Value = value;
}
public T Value { get; private set; }
}
UPDATE: Thanks to the suggestions, the model has now morphed to the following:
public class ParameterRegistration
{
public DateTime RegistrationDate { get; set; }
public IList<ParameterRegistrationValue> ParameterRegistrationValues { get; set; }
}
public abstract class ParameterRegistrationValue()
{
public static ParameterRegistrationValue CreateParameterRegistrationValue(ParameterType type)
{
switch(type)
{
case ParameterType.Integer:
return new ParameterRegistrationValue<Int32>();
case ParameterType.String:
return new ParameterRegistrationValue<String>();
case ParameterType.Guid:
return new ParameterRegistrationValue<Guid>();
default: throw new ArgumentOutOfRangeException("Invalid ParameterType: " + type);
}
}
public Parameter Parameter { get; set; }
}
public class ParameterRegistrationValue<T> : ParameterRegistrationValue
{
public T RegistrationValue {get; set; }
}
public enum ParameterType
{
Integer,
Guid,
String
}
public class Parameter
{
public string ParameterName { get; set; }
public ParameterType ParameterType { get; set;}
}
which is indeed a bit simpler, but now I'm wondering, since the IList in ParameterRegistration points to the abstract ParameterRegistrationValue object, how will I be able to get the actual value out (since its stored on the sub-objects)?
Maybe the whole generic thing is indeed not quite the way to go after all :s

If you don't know the final set of parameter and the corresponding type of each parameter then the generics probably won't help - use object as a parameter value type.
Furthermore iterating through the list of parameters will be a pain since you'll have to examine the type of each item in order to determine how to treat the value.
What are you trying to achieve with generics ? Yes, they are cool (and going for boxing/unboxing is probably not a best idea), but in some cases you might want to use object instead (for both simplicity and flexibility).
-- Pavel

What you might want to introduce is an abstract base class for RegistrationValue<T> that is not generic, so that your ParameterRegistrationValue class can hold a non-generic reference, without needing knowledge of the type involved. Alternatively, it may be appropriate to make ParameterRegistrationValue generic also, and then add a non-generic base class for it instead (so that the list of values in ParameterRegistration can be of different types.
1st way:
public abstract class RegistrationValue
{
}
public class RegistrationValue<T> : RegistrationValue
{
public RegistrationValue(T value)
{
Value = value;
}
public T Value { get; private set; }
}
And now your code should compile.
Once you have a non-generic base class, I'd also move any members of the generic class that don't depend on the generic type parameters up into this base class. There aren't any in this example, but if we were instead modifying ParameterRegistrationValue to be generic, I'd move Parameter up into the non-generic base class (because it doesn't depend on the type parameter for RegistrationValue)

May be, you should use public RegistrationValue RegistrationValue, where T - is type, using in generic. For example, T - is String or other class or struct.
Or you should make class ParameterRegistrationValue as generic, to use generic argument in the field RegistrationValue.

I believe you want to have a collection of instances of different RegistrationValues-derived classes and be able to iterate it and for to have different type for each element. That's rather impossible.
You'll still need to cast each element to the type you know it is, because iterating the collection will return references to your base type (ParameterRegistrationValue - this one specified by IList type parameter). So it won't make any real difference from iterating over non-generic object list.
And if you can safely do that casting for each parameter (you know all the types), you probably don't need collection like this at all - it'll be better to have a class that encapsulates all the parameters in one type, so that you can call it with strong types, with IntelliSense etc. like this:
public class ParameterRegistration
{
public DateTime RegistrationDate { get; set; }
public PatientData PatientData { get; set; }
public Guid Identifier { get; set; }
// ...
}

No base class problem, How to use Castle.DynamicProxy Mixin in this particular case?

I have a 3rd party badly designed library that I must use.
It has all sorts of types it works with, we'll call them SomeType1, SomeType2 etc.
None of those types share a common base class but all have a property named Value with a different return type.
All I want to do is to be able to Mixin this class so I'll be able to call someType1Instance.Value and someType2Instance.Value without caring what the concreate type it is and without caring what the return type is (I can use object).
So my code is currently:
public interface ISomeType<V>
{
V Value {get; set;}
}
public interface ISomeTypeWrapper
{
object Value { get; set; }
}
public class SomeTypeWrapper<T> : ISomeTypeWrapper
where T : ISomeType<???>
{
T someType;
public SomeTypeWrapper(T wrappedSomeType)
{
someType = wrappedSomeType
}
public object Value
{
get { return someType.Value; }
set { someType.Value = value != null ? value : default(T); }
}
}
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
The problem is that I don't know what T might be until runtime due to the fact that I get a dictionary of objects.
I can iterate the dictionary and use reflection to create a SomeWrapperType on runtime but I would like to avoid it.
How can I mixin the concreate type of SomeType to ISomeType?
How can I know what V type parameter is? (wish I had typedefs and decltype like in c++)
How can I, with the minimum of use of reflection possible Mixin those classes with the interface/base class?

You could try the Duck Typing Extensions for Windsor. It means you will need to register each of your types.
container
.Register(Component.For(typeof(SomeType1)).Duck<ISomeType>())
.Register(Component.For(typeof(SomeType2)).Duck<ISomeType>());
You could probably use linq and the register AllTypes syntax to reduce code if the names are similar.
Alternatively in the short term create a factory which can return you the objects you need, implement a concrete object for each type. No you are using the interface you can remove the factory at a later date and replace it with something else with minimal impact:
public class SomeTypeWrapperFactory
{
public ISomeType<int> CreateWrapper(SomeType1 someType1)
{
return new SomeType1Wrapper(someType1);
}
public ISomeType<string> CreateWrapper(SomeType2 someType2)
{
return new SomeType2Wrapper(someType2);
}
}
public class SomeType1Wrapper : ISomeType<int> { ... }
public class SomeType2Wrapper : ISomeType<int> { ... }
Regardless of how you implement the wrapper, be the individually or using a god like class you have the ability to change how the wrapping is done and keep the rest of your code clean.

Why SomeTypeWrapper but not SomeObjectWrapper?
public class SomeObjectWrapper : ISomeType
{
Object _someObject;
PropertyInfo _valuePropertyInfo;
public SomeObjectWrapper(Object wrappedSomeObject)
{
_someObject = wrappedSomeObject;
_valuePropertyInfo = _someObject.GetType().GetProperty("Value", System.Reflection.BindingFlags.Public);
}
public object Value
{
get { return _valuePropertyInfo.GetValue(_someObject, null); }
set { _valuePropertyInfo.SetValue(_someObject, value, null); }
}
}

Edited With .NET 3.5 using LinFu
You may use LinFu instead of Castle. However, you would be using reflection anyway, both with Castle's and with Linfu's DynamicProxy, only hidden in the guts of the libraries instead of being exposed in your code. So if your requirement to avoid the use of reflection is out of performance concerns, you wouldn't really avoid it with this solution.
In that case I would personally choose Orsol's solution.
However: here's an example with LinFu's ducktyping.
public interface ISomeType {
object Value{get; set;}
}
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
public class SomeTypeWrapperFactory
{
public static ISomeType CreateSomeTypeWrapper(object aSomeType)
{
return aSomeType.CreateDuck<ISomeType>();
}
}
class Program
{
public static void Main(string[] args)
{
var someTypes = new object[] {
new SomeType1() {Value=1},
new SomeType2() {Value="test"}
};
foreach(var o in someTypes)
{
Console.WriteLine(SomeTypeWrapperFactory.CreateSomeTypeWrapper(o).Value);
}
Console.ReadLine();
}
}
Since you don't know the type of the SomeType's until runtime, I would not use mixins, but the visitor pattern (I know this doesn't answer the question on how to use mixins for this, but I just thought I'd throw in my 2 cents).
With .NET 4 using dynamic
See Bradley Grainger's post here on using c#4's dynamic keyword to implement the visitor pattern.
In your case, reading all the "Value" properties from your dictionary of SomeType's could work like this:
public class SomeType1
{
public int Value { get; set; }
}
public class SomeType2
{
public string Value { get; set; }
}
public class SomeTypeVisitor
{
public void VisitAll(object[] someTypes)
{
foreach(var o in someTypes) {
// this should be in a try-catch block
Console.WriteLine(((dynamic) o).Value);
}
}
}
class Program
{
public static void Main(string[] args)
{
var someTypes = new object[] {
new SomeType1() {Value=1},
new SomeType2() {Value="test"}
};
var vis = new SomeTypeVisitor();
vis.VisitAll(someTypes);
}
}