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Cast a less specified interface IInterface to a more specified IInterface<TKey,TValue>?

I have two interfaces
public interface ISerializableDictionary { ... }
public interface ISerializableDictionary<TKey,TValue>
: ISerializableDictionary { ... }
I need to cast from the former to the latter at run time using reflection.
It's clearly easy to interrogate the former with GetType().GetGenericArguments.
But how do I then do the cast? I have this code below but it is failing to compile, for the obvious reason that I am trying to use a variable as a type.
Type[] genericTypes = dictionary.GetType().GenericTypeArguments;
Type keyType = genericTypes[0];
Type valueType = genericTypes[1];
// this compiles but doesn't do the cast
Type dictType = typeof(SerializableDictionary<,>).MakeGenericType(keyType, valueType);
var createdDictionary = Activator.CreateInstance(dictType);
// this is the line that won't compile - 'dictionary' is a SerializableDictionary, and I want to access it through its typed generic interface
ISerializableDictionary<keyType,valueType> serializableDictionary = dictionary as ISerializableDictionary<keyType, valueType>;
The more specified interface has a method which I need to call. The less specified interface does not (and can't ever be, because the call needs a typed argument).
Is the solution something to do with dictionary.GetType().GetInterfaces()?
Any steer will be wildly appreciated. Programming solo at the moment so I don't have a team to call on, hence the query here.
UPDATE - in response to comments
The problem I am trying to solve is how to serialize members of an object where the members are themselves enumerable. I am trying to figure out how serialization libraries do it as a learning exercise and because I have a few ideas that I want to explore. Serialization & Reflection are not my main areas of programming so I am stumbling to learn them.
So I have (as reduced code):
public class ExperimentalSerializer<T>
{
public void Serialize(T objectToSerialize)
{
IEnumerable<object> collectionsToSerializeToCSV = objectToSerialize.GetEnumerableMembers();
foreach (object collectionToSerialize in collectionsToSerializeToCSV)
{
string csvString = "";
if (collectionToSerialize.IsDictionary())
{
// serialize dictionary here to csvString
// but cannot properly access contents through just IDictionary
// need IDictionary<TKey,TValue>
// ** ALSO SEE TEXT BELOW THIS CODE SNIPPET**
}
else if (collectionToSerialize.IsList())
{
// serialize list here to csvString
}
else if (collectionToSerialize.GetType().IsArray)
{
// serialize array here to csvString
}
// save csvString to somewhere useful here
}
}
}
And elsewhere I have an extension method:
public static IEnumerable<object> GetEnumerableMembers(this object objectToInterrogate)
{
Type objectType = objectToInterrogate.GetType();
// get the enumerable properties
PropertyInfo[] properties = objectType.GetProperties(BindingFlags.Instance | BindingFlags.Public);
IEnumerable<PropertyInfo> enumerableProperties = properties.Where(propertInfo => propertInfo.PropertyType.GetInterfaces().Any(x => x == typeof(IEnumerable)));
IEnumerable<PropertyInfo> serializableProperties = enumerableProperties.Where(p => p.IsSerializable());
IEnumerable<object> enumerablePropertyValues = serializableProperties.Select(p => p.GetValue(objectToInterrogate, null));
// get the enumerable fields
FieldInfo[] fields = objectType.GetFields(BindingFlags.Instance | BindingFlags.Public);
IEnumerable<FieldInfo> enumerablefields = fields.Where(propertInfo => propertInfo.FieldType.GetInterfaces().Any(x => x == typeof(IEnumerable)));
IEnumerable<object> enumerablefieldValues = enumerablefields.Select(f => f.GetValue(objectToInterrogate));
// merge the two lists together
IEnumerable<object> enumerableMembers = enumerablePropertyValues.Union(enumerablefieldValues);
return enumerableMembers.ToList();
}
One specific challenge I am investigating is how to serialize an enumerable (Dictionary, List or array TValue[]) where TValue is itself a complex type (e.g. a class that can be serialized). This cannot be ascertained without knowing the type of TValue, but this cannot be retrieved from IDictionary or IList alone and these can only be enumerated with the type object.
This is the very specific point I am trying to investigate and potentially to control: how to determine TValue and then to work out if/how to serialize it in turn. My idea is to cast to more-specified generics with known type parameters but I get a bit lost at this point.
Hope this helps.

#SLaks points out in the comments:
Casting is inherently a compile-time operation. Casting to a type only known at runtime makes no sense. You can't call your method if its types are not known at compile-time.
That's absolutely right. You can, of course, still call the intended method at runtime, but you'll need to use (more) reflection to do it, since you have no way to get the compiler to generate a statically-typed call.
To do this, take the Type object you already constructed using MakeGenericType(), and call GetMethod() on it to get the Type.MethodInfo object corresponding to the method to call. Then, call MethodInfo.Invoke().
Type dictType = typeof(SerializableDictionary<,>).MakeGenericType(keyType, valueType);
MethodInfo method = dictType.GetMethod("MyMethod");
object returnValue = method.Invoke(dictionary, new object[] { /* arguments */ });
TMI...
When you write dictionary.MyMethod(), the C# compiler generates a Callvirt IL (byte code) instruction. The object to call the method on (and the arguments to the method) are pushed onto the stack, and the argument to Callvirt is the metadata token corresponding to the type-qualified ISerializableDictionary<TKey,TValue>.MyMethod method. This is the normal calling mechanism in .NET. When you (and the compiler) don't know what TKey and TValue are at compile time, there's no way to get the right metadata token for the method, and no way to generate the Callvirt. That's why you have to use the reflection API.
You can, however, use something like DynamicMethod to generate your own IL and JIT it at runtime. Once JITted, the call is just as fast as one statically generated by the compiler. There is of course significant overhead to generating a dynamic method, but it's a one-time overhead.
Of course, #DavidL points out:
The approach here seems wildly off-course. Instead of asking for a specific solution, can you please describe the specific concrete problem that you are trying to solve?
That, too, is absolutely right. So don't do what I just suggested unless you really, really know what you're doing and have a really, really good reason. (Hint: You don't.) But I thought this information might give you a better overall picture of why you can't do what you expected to do.

Create list of generic object at runtime

I have object of some type known at runtime and I read and deserialize this object from database. It works. Now I would like to add it to some list:
private static List<T> generateList<T>()
{
List<T> lst = new List<T>();
return lst;
}
private void readObjects(System.Type objType)
{
var methodInfo = typeof(My.Serializator).GetMethod("DeserializeDb");
var genericMethod = methodInfo.MakeGenericMethod(objType1);
List<curType> currentList= generateList<curType>();
// ...read stream from database and convert it to object
while (_rs.Read())
{
var _objItem = genericMethod.Invoke(null, new[] { _streamedData });
currentList.Add(_objItem);
}
}
It won't work. The error is:
curType is a variable but is used like a type.
If I change list to:
List<object> currentList = new List<object>();
it will work. But can i do this with generics(T) instead of object type?

You can easly create type of list you want via Activator, then cast to IList and use it:
private IList readObjects(System.Type objType)
{
var listType = typeof(List<>).MakeGenericType(curType);
var list = (IList)Activator.CreateInstance(listType);
// ...
while (_rs.Read())
{
// ...
list.Add(_objItem);
}
}
list will be instance of List<YorActualType>.
Update
When you declaring your method with generic arguments, it assumes you provide type info during compile time. Otherwise you need to use reflection.
Since you providing type info in run time (curType can hold any type info), compiler does not know what exactly type will be used, and you cannot declare your method to return something concrete. Only abstractions allowed.
Let's me show it on slightly insane but demonstrative example:
var types = new [] { typeof(int), typeof(string) };
var rand = new Random();
var list = readObjects(types[rand.Next(0,2)];
Until the very last moment even you will not know what exactly type of list will be created. Compiler does not know too. Compiler will never know what exactly type should be used if you not provide him with you types. When you use Type it only tells compiler that some regular parameter with type Type will be passed into the method in run time. There is no data to infer a type during compile time. That data can be passed only via generic type parameters.
So, there is several ways you can follow:
Provide exact types you need at compile time
private List<T> readObjects<T>()
{
var objType = typeof(T);
var list = new List<T>();
// rest of code....
}
Use reflection and base types
private IList readObjects(Type objType)
{
// rest of code with Activator and so on
}
And later usage depends on your needs.
If you know what type you going to use, simply convert:
var list = (IList<MyType>)readObjects(typeof(myType));
But I guess in that case better use way #1 with generic argument.
Otherwise you going to use reflection. Or some base classes, interfaces and so on. It depends on what exactly task you going to solve.
P.S. You can read more about generic types on MSDN.

Casting List<[KnownType]> to List<T> to match function's return type?

I am trying to make a function that generically retrieves data from my MongoDB collections. To do this I have constructed a generic method that returns a List<T>.
My issue is that I have to create this List<T> to return, but I do so based on the typeof T. I am not sure what I need to do to please the compiler..
public async Task<List<T>> GetDocsAsync<T>(
CollectionTypes collection, // Enum representing my Collections
FilterDefinition<BsonDocument> search,
SortDefinition<BsonDocument> sort = null)
{
// Get BsonDocuments from the collection based on the search and sort criteria
List<BsonDocument> matchedDocs;
IMongoCollection<BsonDocument> MongoCollection = GetCollection(collection);
if (sort == null) matchedDocs = await MongoCollection.Find(search).ToListAsync();
else matchedDocs = await MongoCollection.Find(search).Sort(sort).ToListAsync();
// Return a List<T>, covert matchedDocs to List<T> if need be
Type docType = typeof(T);
if (docType == typeof(BsonDocument))
return matchedDocs;
else if (docType == typeof(LogEvent_DBDoc))
return LogEvent_DBDoc.ConvertFromBson(matchedDocs);
// ...
}
At both of the return lines I receive an error along the lines of "Cannot implicitly convert from List<[KnownType]> to List<T>. Which makes sense to me, because the typeof T does not necessarily match the typeof say BsonDocument. But I have made the proper check to do so.
Can I cast List<[KnownType]> to List<T>?

You are abusing generic syntax. Generic code should be generic, i.e. work with whatever type you use.
You should have different methods, depending on the type that will be passed in. By all means, make the truly generic parts into its own generic method, which your type-specific methods can call. But have the caller, who already knows what type it's using, pick the appropriate method based on that type, and then just use that type explicitly in each type-specific method.
It's hard to say with the example you have, but if you can provide a good Minimal, Complete, and Verifiable example that shows clearly what you're doing, I would be happy to refactor it to show what I mean.

If you're sure you have the List<KnownType> that matches the type of current generic instantiation of List<T> you can cast it to the required generic type with the help of intermediate cast to object:
List<T> GetListOf<T>() {
if (typeof(T) == typeof(String)) {
var stringList = new List<String> { "a", "b" };
return (List<T>)(object)stringList;
}
throw new NotSupportedException();
}
Leaving the moral judgement whether you should do so to yourself )

How do I use the Type from my List<Type>?

I would like to make my code convention-based by using Types and keeping things simple, but generics has it's own complexity with it's own learning curve.
I have a bunch of POCOs (Plain Old CLR Objects) in a List that I'd like to iterate through later in the code.
var models = new List<Type>();
models.Add(typeof(Person));
models.Add(typeof(Company));
Would like to cycle through each list item:
models.ForEach(m =>
{
var label = m.FullName;
// var data = JsonConvert.DeserializeObject<List<typeof(m)>>(""); // doesn't work
var data = JsonConvert.DeserializeObject<List<m>>(""); // doesn't work either
...
}
The issue is that the "m" in the Deserialize line isn't working. What would be the best way to pass that through, i.e. making the 'List<m>' a 'List<T>' that we can use?

To use generics, you really need to know the Type (T) at compile time, you don't - you know it at run time. (Caveat: Its possible with reflection, but theres no need to use it when there's an overload as described below)
There is an overload of DeserializeObject which takes a Type rather than use generics. So your code would be
models.ForEach(m =>
{
var label = m.FullName;
var data = JsonConvert.DeserializeObject("",m);
...
}
However, as you've pointed out in comments you actually need a List<T> not a single T. You'll need a little bit of reflection, just to create the right type to pass to the above DeserializeObject call.
var tList = typeof(List<>); // Type of open List
models.ForEach(m =>
{
var label = m.FullName;
var tConvert = = tList.MakeGenericType(m);
var data = JsonConvert.DeserializeObject("",tConvert);
...
}
The answer to your question is above, but the more I look at it the harder it is to see what you can actually do with data. all you'll ever know about data is that it is an object. You cant cast it to anything - you wont know if its a list of Person or a list of Company.
Perhaps this was an overly contrived example you've used for a real-life problem. If not I forsee you're next problem is what to do with data!!

If you don't know the type at compile time you can do this with Reflection. Consider the following code:
models.ForEach(m =>
{
var mi = JsonConvert.GetType()
.GetMethod("DeserializeObject");
var m = mi.MakeGenericMethod(new[] { m });
// you pass [null] for the object because it's a [static] method
// and you don't have to declare [args] if you can express it simply
// but keep in mind that it's simply an object[]
m.Invoke(null, args);
}

Another solution is to call the generic method using reflection (if there isn't any overload that takes the type as parameter)
models.ForEach(m =>
{
MethodInfo method = typeof(JsonConvert).GetMethod("DeserializeObject");
MethodInfo generic = method.MakeGenericMethod(m);
generic.Invoke(null, "");
}

Declare a generic type instance dynamically [duplicate]

This question already has answers here:
How do I use reflection to call a generic method?
(8 answers)
Closed 9 years ago.
Is it possible to declare an instance of a generic without knowing the type at design-time?
Example:
Int i = 1;
List<typeof(i)> list = new List<typeof(i)>();
where the type of i could be anything, instead of having to do:
List<int> list = new List<int();

If you don't know the type at compile-time, but you want the actual type (i.e. not List<object>) and you're not in a generic method/type with the appropriate type parameter, then you have to use reflection.
To make the reflection simpler, I've sometimes introduced a new generic type or method in my own code, so I can call that by reflection but then just use normal generics after that. For example:
object x = GetObjectFromSomewhere();
// I want to create a List<?> containing the existing
// object, but strongly typed to the "right" type depending
// on the type of the value of x
MethodInfo method = GetType().GetMethod("BuildListHelper");
method = method.MakeGenericMethod(new Type[] { x.GetType() });
object list = method.Invoke(this, new object[] { x });
// Later
public IList<T> BuildListHelper<T>(T item)
{
List<T> list = new List<T>();
list.Add(item);
return list;
}
Of course, you can't do an awful lot with the list afterwards if you don't know the type... that's why this kind of thing often falls down. Not always though - I've used something like the above on a few occasions, where the type system just doesn't quite let me express everything I need to statically.
EDIT: Note that although I'm calling Type.GetMethod in the code above, if you were going to execute it a lot you'd probably want to just call it once - after all, the method isn't going to change. You may be able to make it static (you could in the case above) and you probably want to make it private too. I left it as a public instance method for the simplicity of the GetMethod call in sample code - you'd need to specify the appropriate binding flags otherwise.

If you don't know the type at design-time, I'd say you have a list of OBJECTS (the base class for all other types).
List<object> list = new List<object>();

I think the best you are going to be able to do is something like this:
static void Main(string[] args)
{
int i = 1;
var thelist = CreateList(i);
}
public static List<T> CreateList<T>(T t)
{
return new List<T>();
}

You can also use Activator.CreateInstance. Example code snippet:
public class BaseRepository<T> where T : DataContext
{
protected T _dc;
public BaseRepository(string connectionString)
{
_dc = (T) Activator.CreateInstance(typeof(T), connectionString);
}
public void SubmitChanges()
{
_dc.SubmitChanges();
}
}

If you still want to type .Add(), .Remove(), do foreach etc. you can treat the List as a regular "old" System.Collections.IList,
since this interface is luckily implemented by List<T>.
And since all other posted answers to this question shows pretty much every other possible way to create an instance of a List<T> dynamically,
i will show one last way to do it.
I personally use this method when creating generic instances, when i don't really know nothing about the type at compile time,
and the type must be passed as a string, perhaps coming from the application configuration file.
In this example, T is System.String for simplicity but it could be anything:
Type T = typeof ( string ); // replace with actual T
string typeName = string.Format (
"System.Collections.Generic.List`1[[{0}]], mscorlib", T.AssemblyQualifiedName );
IList list = Activator.CreateInstance ( Type.GetType ( typeName ) )
as IList;
System.Diagnostics.Debug.Assert ( list != null ); //
list.Add ( "string 1" ); // new T
list.Add ( "string 2" ); // new T
foreach ( object item in list )
{
Console.WriteLine ( "item: {0}", item );
}