C#: How to perform 'as' operation with a Type

Question

I want to test whether a given object can be cast to a given Type.

In this scenario, I have an object, and the Type representing what type I want to cast it to:

public function FooBar(..., object data, Type expected) {
    ...
    var unboxedData = ?
    if (unboxedData == null) {
       ....
    }
    ...
}

How can I cast data to the type type represents?

Basically, I want to do this:

    var unboxedData = data as Type;

...but of course you can't use Type with an as statement, so what do I do?

Answer 1

Edit 2: I'm going to say it's not possible without reflection or generics. With reflection, you have no compile-time checking and must use reflection (or dynamic) to further call methods/properties of the object. With generics, you can't use a Type object to get there alone. Take your pick. Is it possible to refactor your calling code to allow generics?

---

If allowed, this may be more easily handled with a generic method:

public resultType FooBar<T>(..., object data) {
    ...
    T unboxedData = (T)data;
    ...
}

Edit: Also, you can use data as T if you include a generic type constraint of where T : class:

public something FooBar<T>(..., object data)
    where T : class
{
    ...
    T unboxedData = data as T;
    if (unboxedData == null) {
        ...
    }
    ...
}

Answer 2

...but of course you can't use Type with an as statement, so what do I do?

Morre importantly, you can't use var this way. So there is nothing to be gained here.

You can test if it's the right type with

 if (expected.IsInstanceOfType(data))

But then you still can't write any decent code to access properties or methods on data.

Answer 3

C# provides the as keyword to quickly determine at runtime whether a given type is compatible with another. When you use the as keyword, you are able to determine compatibility by checking against a null return value. Consider the following:

Hexagon hex2 = frank as Hexagon;

if (hex2 == null)
    Console.WriteLine("Sorry, frank is not a Hexagon...");

In addition to the as keyword, the C# language provides the is keyword to determine whether two items are compatible. Unlike the as keyword, however, the is keyword returns false, rather than a null reference, if the types are incompatible.

if (emp is SalesPerson)
{
    Console.WriteLine("{0} made {1} sale(s)!", emp.Name, 
                                              ((SalesPerson)emp).SalesNumber);
}