Dynamic generic cast at runtime

I understand what you're getting at, the closest you can get is using ChangeType, this will give you your runtime exceptions you are looking for, but you'll have to use objects again:
Type myType = Type.GetType("System.Int32");
object testInt = Convert.ChangeType(100, myType);
testInt = Convert.ChangeType("testing", myType);   // throws runtime exception

I am trying to create a SortedList where T1, T2 are know only at runtime. I do not think this is going to be possible in C# .NET though. SortedList might be the best solution, although it is not very nice because there is so much boxing and no type checking of the Value type.

Originally I thought/hoped that "Type" could be used like this:

Type myType = typeof(int);
myType intVariable;

intVariable = 100; // checked at run time, okay because 100 is int
intVariable= "a string"; // compiles but checked at run time, generates runtime error.

// or even...
typeof(string) stringVariable;

stringVariable = 100; // run time error
stringVariable= "a string"; // okay

Generics aren't necessarily meant to for types declared at runtime, think about a generic list for example, instead of having each typed list being it's own type, eg. IntegerList, StringList, DoubleList; we have a generic list List, now you have all the list methods (add, remove, sort, etc...) declared in one generic class, but it can be applied to any type you feed the list without having to write seperate classes for each type. What exactly are you trying to achieve?

Here is one idea, but it is not very nice.

        public class RuntimeSortedList
        {
            Type KeyType;
            Type ValueType;
            public object theList;

            // Will need to define a method info for each member of SortedList<,>
            MethodInfo AddMI;

            public RuntimeSortedList(Type KeyType, Type ValueType)
            {
                this.KeyType = KeyType;
                this.ValueType = ValueType;

                // Make a "Type" called General which is "any kind of SortedList"
                Type General = typeof(SortedList<,>);

                // make a more specific type
                Type specific = General.MakeGenericType(new Type[] { KeyType, ValueType });

                // create an instance of specific
                theList = Activator.CreateInstance(specific);

                // Define wrappers to expose every SortedList<,> member
                AddMI = specific.GetMethod("Add");
            }

            // Define wrappers to expose every SortedList<,> member
            public void Add(object Key, object Value)
            {
                if (Key.GetType() != KeyType) throw new Exception(string.Format("Key is type {0}, should be {1}.", Key.GetType(), KeyType));
                if (Value.GetType() != ValueType) throw new Exception(string.Format("Value is type {0}, should be {1}.", Value.GetType(), ValueType));
                AddMI.Invoke( theList, new object [] {Key, Value});
            }
        }


        static void Main(string[] args)
        {

            RuntimeSortedList rtsl = new RuntimeSortedList(typeof(long), typeof(string));

            // Bit annoying that 100 goes in as Int32 because we are passing as "object".
            rtsl.Add(100L, "massive bixing overhead?");
        }

I just don't get it! What is the point in being able to create the object "myList"? There does not appear to be any way to do anything to it related to the fact that it is a SortedList. 

Any ideas?

Thanks,
Matthew.

I could use SortedList but I feel that defeats the object of generics. A) I loose type checking. B) I would gain the boxing/unboxing overhead.

Will SortedList work for what you need to do?
SortedList<object, object> genericList = new SortedList<object,object>();
genericList.Add(100, "hooray!");
 
Note: if you try to add another element to your list where the key type is different than the first, you'll get an exception.