How to declare an instance which its type is user-defined in C#

Question

Hey all,

Simply my question is about defining the type of an instance in run time, and this type is user-defined. Something which looks like this:

Type instance1;

In run time, the user is going to choose for example "int", then there 'll be,

int instance1;

Any suggestions?? is downCasting efficient here?

Answer 1

What you are looking for are generics. Read an introduction here.

For example you would declare the class, you want that user defined type to be in, like that:

class MyClass<T>
{
    private T instance1 = default(T);

    public MyClass(T initalvalue)
    {
        instance1 = initalvalue;
    }

    //... some more code
}

Answer 2

Without you explaining more details of what you are looking to accomplish, you can either use a generic method^*, you can use C# 4's dynamic keyword, or you can use reflection to create instances of the given type.

^*The generic method will work well if the type can be known at compile-time or if it's one of only a finite set of types, and you'll pick a type that was named at compile-time (i.e. user will say one of int, char, or double, and you'll use the correct generic accordingly). If it's completely indeterminable, you'll still need to use reflection to instantiate the generic with the type given at run time.

Answer 3

dynamic Keyword in C# 4.0

Answer 4

I presume, this is what you are looking for:

Type myType = typeof(int);
int value = Activatior.CreateInstance(myType);

In .NET 4, the dynamic keyword is perhaps more effective and convenient.