.NET reflection cast to exact type

Question

i wonder if there is a way to cast to exact type using system.reflection so that you will avoid doing explicit cast such as

(System.DateTime)

for example

Assuming i would have a Dictionary such as

Dictionary<propName, Dictionary<object, Type>>

and assuming i iterate over an object props list

foreach (var prop in @object.GetType().GetProperties())
{
       object propValue = propInfo.GetValue(@object, null);
       string propName = propInfo.Name;

       Dictionary<object, Type> typeDictionary = new Dictionary<object, Type>();
       Type propType = propInfo.GetValue(@object, null).GetType();
       typeDictionary[propValue ] = propType ;

       propsDictionary[propInfo.Name] = propValue;
}

I would like to do something like , cast to exact type using something like

// this part is only for guidelines 
// it should obtain the exact Type 
// ... but it returns a string of that type Namespace.Type
Type exactType = Dictionary[enumOfPropName][someValue] 
// this part should know the exact type Int32 for example and cast to exact 
var propX = (exactType)someValue

Is there any way of doing such thing and if so how can i obtain this? Also most of this code is just a guideline, an idea so please don't take it likely. Thank you all.

http://stackoverflow.com/questions/4010144/convert-variable-to-type-only-known-at-run-time — stuartd, Aug 11 '16 at 12:33
Casting requires a statically known type to cast to. You don't need to do dynamic casting since the runtime type of `someValue` is known by the runtime. What could you do with `propX` given you don't know the static type? — Lee, Aug 11 '16 at 12:37

score 5 · Accepted Answer · answered Aug 11 '16 at 12:37

An object's type is runtime information.
A variable's type is compile-time information.
Compile-time comes before runtime.

The conclusion here is that it's not possible to have a statically typed variable that matches the exact type of an arbitrary object instance, because doing so would require information that is not available yet.

As a workaround, consider making the variable dynamic and see what you can do from there.

MattC · Answer 2 · 2016-08-11T13:41:41.233

4

Once you know the type:

var x = 22;
var type = typeof(Int32);
var propX = Convert.ChangeType(x, type);

Or in your case:

object thing = 32;
var lookup = new Dictionary<string, Dictionary<object, Type>>();

lookup.Add("Test", new Dictionary<object, Type>());

lookup["Test"].Add(thing, typeof(Int32));

var propX = Convert.ChangeType(thing, lookup["Test"][thing]);

Caveats with this approach: Convert.ChangeType: For the conversion to succeed, value must implement the IConvertible interface...

edited Aug 11 '16 at 13:41

answered Aug 11 '16 at 12:33

MattC

3,984
1
33
49

2

I don't think this covers a list of properties of random types, which, to my uderstanding is what is being asked. – Zalomon Aug 11 '16 at 12:35
It's a limited solution. If the OP uses custom types which don't implement IConvertible, this solution can't work: [Convert.ChangeType](https://msdn.microsoft.com/en-us/library/dtb69x08(v=vs.110).aspx) – romain-aga Aug 11 '16 at 13:33
Agreed, I just followed on from what the OP said he wanted to do. – MattC Aug 11 '16 at 13:35
1

You might edit your post to signal this specification to the OP. ;) – romain-aga Aug 11 '16 at 13:38

score 0 · Answer 3 · answered Aug 11 '16 at 12:40

If I understand your question, you want to convert an object (in an object typed variable) to its actual type you have extracted thorough reflexion. If so, I beleive Convert.ChangeType could be of help to you. You can use it like this :

var propX = Convert.ChangeType(someValue, exactType);

I am pretty casting requires you to know the type at compile-time, which is why you cannot cast with a Type variable (since it's only known at runtime).

score -1 · Answer 4 · answered Aug 11 '16 at 12:35

You will need to implement an implicit operator on the target class to the type you want

class Program
{
    static void Main(string[] args)
    {
        var a = new A() { property = "someValue" };
        string obj = (string)teste;
    }
}

class A
{
    public string property { get; set; }

    public static implicit operator string(A t)
    {
        if (t == null)
            return null;

        return t.property;
    }
}

.NET reflection cast to exact type

4 Answers4