Get static type of x in C#?

Question

I have this class structure :

class A     {   }
class B:A   {   }

A x = new B();

this is the runtime type :

x.GetType(); //B

How can i get its compile time type ?

I tried typeof (x) - but the argument has to be a type...

my desire answer is : A

edit

why am i asking it ?

cause i think int is inistialized via polymorphic engine :

something like this :

object myInd = new Int32(); / /this DOES compile

and i want to verify my assumption :

does it come from object ?

and in order to do it - i have to know its static type....

Could you provide a bit of context? I fail to see a use-case for this, since the compile-time type is always known to the developer... — Heinzi, May 27 '12 at 19:00
@HansPassant Hans , I already know that. i just want the answer via code... — Royi Namir, May 27 '12 at 19:01
possible duplicate of [How to know in C# code which type a variable was declared with](http://stackoverflow.com/questions/1786750/how-to-know-in-c-sharp-code-which-type-a-variable-was-declared-with) — BoltClock, May 27 '12 at 19:04
@Heinzi: The type is not always known to the developer. Consider `var` variable assigned to by a function. Although you can check the function return type, you don't always want to depend on that. — Daniel, May 27 '12 at 19:08
I understand what you're asking, but not why. Usually all you need to care about is what the variable is at run time, e.g. `x is B`. I don't see where you should code differently depending on whether the caller has `A x = new B();` or `B x = new B();`. — Tim S., May 27 '12 at 19:41

score 12 · Accepted Answer · answered May 27 '12 at 19:04

12

You can create a generic method:

Type StaticTypeOf<T>(T t)
{
  return typeof(T);
}

To call it:

object i = 1;

// Writes out System.Object
Console.WriteLine(StaticTypeOf(i).ToString());

It's a solution - even though I don't see what the problem solved with the solution is ;-)

answered May 27 '12 at 19:04

Anders Abel

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Actually you dont need `...(T t)`! – Felix K. May 27 '12 at 19:08
2

Then you'd have to say `StaticTypeOf – Tim S. May 27 '12 at 19:36
1

Correct but hardly useful... You're just using the compiler feature of type inference to tell you what you already know - that `i` is of type `object`. – jeroenh May 27 '12 at 20:30
1

@jeroenh: I don't understand the use for this either, but apparently Royi Namir has a use for it so I helped him with the solution. – Anders Abel May 27 '12 at 20:33

score 1 · Answer 2 · answered May 27 '12 at 20:21

1

As stated in comments by others - the static type of an object is something you tell the compiler yourself, at compile time. There is absolutely no point in finding it out at runtime.

object myInd = new Int32(); / /this DOES compile

This compiles not because "int is initialized via a polymorphic engine", but because in C# everything can be converted to type object. This is not the same.

The conversion from a value type (such as Int32) to object is realized through the process of boxing. You can read all about it on this msdn page: http://msdn.microsoft.com/en-us/library/yz2be5wk.aspx.

answered May 27 '12 at 20:21

jeroenh

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you didnt understand my question at all !. ok it is a boxed value. i know that. but when i write `object i=5` and later `i.Equals(3)` - the equals is resolved at RUNTIME via virtual function from the object ! so the chain starts from object downto int32... the equlas can be started at `int i=5;` and also `object i=5` - but the chain in the former will start at the object level and in the latter it will start from `int`. i needed to check that. – Royi Namir May 28 '12 at 05:47
Indeed everything incl. value types is derived from System.Object, but that has nothing to do with the compile time type. My answer stands: the compile time type is what you write yourself, there is no point in finding it out at runtime. See also http://stackoverflow.com/questions/436211/is-everything-in-net-an-object/436246 – jeroenh May 28 '12 at 08:52

Get static type of x in C#?

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2 Answers2