Is everything in .NET an object?

Question

Please help us settle the: controversy? Is everything in c# an object, I thought that was the case as everything in Visual Studio at least appears as a struct? Please post a reference so that it doesn't become "modern jackass" (this American life).

Note that this question reffers to C# not necessarily .NET and how it handles the data under the hood (obviously it's all 1's and 0's.)

Here are the comments to "everything is an object":

• Eh, no, it's not. – Binary Worrier
• I'd like an example... – scotty2012
• isn't everything derived from the base type Object? – rizzle
• Most things are objects... – Omar Kooheji
• Value types, ints, doubles, object references (not the objects them selves) etc aren't objects. They can be "boxed" to look like objects (e.g. i.ToString()) but really they're primitive types. Change the entry to "NEARLY everthing is an object" and I'll remove the downvote – Binary Worrier
• I appreciate the clarification. I think the lowest level that you can interact with, say an int, in c# is as a struct, which isn't an object? - http://msdn.microsoft.com/en-us/library/ms173109.aspx – rizzle
• Doesn't Int32 inherit from ValueType which inherits from Object? If so, despite the behavior, an int is an object. – Chris Farmer
• No, the boxed type for int inherits from ValueType, which inherits from Object. They're not objects in the traditional sense because a) an int isn't a reference to an int, IT IS the int. b) ints aren't garbage collected. If you declare an Int32, then that int is 4 bytes on the stack, end of story – Binary Worrier

EDIT CLARIFICATION: Definition of object: "Object" as a inheritor of class System.Object vs. "object" as an instance of a type vs. "object" as a reference type."

Answer 1

The problem here is that this is really two questions - one question is about inheritance, in which case the answer is "nearly everything", and the other is about reference type vs value type/memory/boxing, which case the answer is "no".

Inheritance:

In C#, the following is true:

• All value types, including enums and nullable types, are derived from System.Object.
• All class, array, and delegate types are derived from System.Object.
• Interface types are not derived from System.Object. They are all convertible to System.Object, but interfaces only derive from other interface types, and System.Object is not an interface type.
• No pointer types derive from System.Object, nor are any of them directly convertible to System.Object.
• "Open" type parameter types are also not derived from System.Object. Type parameter types are not derived from anything; type arguments are constrained to be derived from the effective base class, but they themselves are not "derived" from anything.

From the MSDN entry for System.Object:

Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.

Languages typically do not require a class to declare inheritance from Object because the inheritance is implicit.

Because all classes in the .NET Framework are derived from Object, every method defined in the Object class is available in all objects in the system. Derived classes can and do override some of these methods.

So not every type in C# is derived from System.Object. And even for those types that are, you still need to note the difference between reference types and value types, as they are treated very differently.

Boxing:

While value types do inherit from System.Object, they are treated differently in memory from reference types, and the semantics of how they are passed through methods in your code are different as well. Indeed, a value type is not treated as an Object (a reference type), until you explicitly instruct your application to do so by boxing it as a reference type. See more information about boxing in C# here.

Answer 2

Based on all books that I read, everything in C# is an object.

Some are reference other are Value type. Value type object inherit from the class ValueType. They have different behavior but inherently ... objects.

This is the reason why you can store an Int32 in an object variable as well as everything that you can ever create in .NET.

For more detail... look at the following: http://msdn.microsoft.com/en-us/library/s1ax56ch(VS.71).aspx

All value types are derived implicitly from the Object class.

Answer 3

Value types are not objects, they obey different copying semantics, different passing semantics, and must be wrapped in a class (Object) in order to be treated as such.

Edit: I think the argument is somewhat vague, as you must qualify what you mean by 'object'. Is an object just something that inherits from Object, or is it something that obeys Object's use semantics? Or are we talking the most general definition of object, where it is anything that can contain data and operations on that data?

Answer 4

The number 2 is not an object.

Answer 5

Your confusing an object with a value or reference. Basically everything is an object. an Int is an object, but a value type. A class instance is an object, but a reference type. Methods aren't objects, nor are properties. The just operate on objects. And yes, pretty much everything inherits from the object class.

Answer 6

I thought that value types are NOT objects. They're stored differently in memory by the CLR - value types are stored on the stack, and objects are stored on the heap. You can cast value types to a reference type to make them act like an object, but the CLR takes the value off of the stack, wraps it in an object, and stores it on the heap. That is what happens when you "box" a variable.

Answer 7

They are all treated as objects, but they are not all objects. The confusion comes in with Autoboxing.

See this for more information: http://en.wikipedia.org/wiki/Object_type

The abstraction confuses people apparently.

Answer 8

The question is not well defined. In C# (and in OOP in general) we have types (class - reference, struct - value, etc.) - these are the definitions. And the "object" is the concrete instance of a given type.

So, if we read the question literally - yes - everything is an object when instantiated.

The confusion most probably begins with a bad choosing of the name of the very base class for everything - in .Net this is the Object class.

Answer 9

Hi all, I'm bowing out of this discussion, all I can bring to it is opinion, the "facts" I had were flawed.

I tried to correct this post, but found

• It would do little good for anyone other than me
• It would take too long, it actually needs to be rewritten and I don't have the time (and even if I did I'm not sure I'd get it right)

Thanks to Konrad Rudolph & Jon Skeet, for making me thing more deeply about what I was saying, and for pointing out where I was wrong. You guys - and the other good folks at SO - are making me raise my game, and be more careful of the "facts" I share :)

Later dudes and thanks again,

BW

P.S. I'm marking this as a wiki answer, it doesn't answer anything at all, but I wouldn't mind leaving it here as a reminder for myself.

Answer 10

Some people here have a strange notion of what an “object” in object-oriented programming is. In order for something to be an object it does not have to be a reference type or, more generally, follow any formal implementation.

All that means is that you can operate on it as a first-class citizen in an object-oriented world. Since you can do this on values in C# (thanks to autoboxing), everything is indeed an object. To some extend, this is even true for functions (but arguably not for classes).

Whether this is relevant in practice is another question but this is a general problem with OOP that I notice once again. Nobody is clear on the definition of OOP (yes, most people agree that it has something to do with polymorphism, inheritance and encapsulation, some throw in “abstraction” for good measure).

From a usage point of view, every value in C# handles like an object. That said, I like the currently accepted answer. It offers both technically important aspects.

Notice that in other contexts, e.g. C++, other aspects are stressed since C++ isn't necessarily object-oriented and furthermore is much more focused on low-level aspects. Therefore, the distinction between objects, POD and builtin primitives makes sometimes sense (then again, sometimes not).

Answer 11

C# has was is referred to as a unified type system. That means that everything can be seen as an object. However, underneath this there are two different types: value types and reference types. Value types can be viewed as an object via the boxing mechanism. This means that an object is created representing the value of the value type in question.

Answer 12

Considering that the question is referring to Object in a OOP sense, the answers is:

From a technical point of view the answer is: No

From a dogmatic point of view the answer is: Yes

Explanation:

Technically value types (primitives or structs) are not objects unless in "boxed" form, but because the .Net does seamless conversions of value types to their Object counterpart through the act of boxing/unboxing (creating a class instance that holds the value and is derived from Object) that means value types can be treated as both objects and simple values.

So value types are dual in nature, they behave as values and as objects. Values in .Net are Objects when they need to be, and they are not objects in the rest of cases.

The correct answer that takes the technical aspect into consideration is "Everything in .Net is as if it were an Object".

The dogmatic answer is "Everything is an Object".

Answer 13

Depends what you mean by "everything" and by "is an object". If you define these two terms, the answer is easy :-)

For example, in some languages an if-block is an object that can be passed around as a value, assigned to a variable and so on. This is not the case in C#, so clearly not everything is an object in C#.

Answer 14

While everyone seems to be focusing on the value types vs. reference types debate, we are forgetting one type in C# that is neither reference nor value, it doesn't derive from object, and it can't be cast to object: pointers.

Unlike values and reference types, pointers cannot be cast to object.

According to the MSDN documentation on C# pointer types,

Pointer types do not inherit from object and no conversions exist between pointer types and object. Also, boxing and unboxing do not support pointers. However, you can convert between different pointer types and between pointer types and integral types.

Answer 15

This a discussion of two worlds: language and memory.

To me language is like a layer of abstraction and the term object belongs to this level of abstraction. I don't see a point in talking about objects in terms of memeory organisation and if you do use the "object" term when talking about memory you actually are borrowing this term from a different layer of abstraction. Thus you shouldn't forget where it came from.

If we're talking about C# I don't undestand why someone would use memory organisation as an argument. Of course if I would answer this question to someone I would say "Yes, in C# everything is an object, but you also should know that under the hood it may work differently depending on...."

This may start an interesting argument but may also speak to some: in a similar discussion one could say that actually there is no object oriented programming, there's only procedural programming. Does you CPU understand objects? Even better, actually there is no software, there's only differnt hardware states :)

My point is that some terms don't translate to other layers of abstraction and you should stick the discussion to where it belongs (which in this case is a language, not memory).

Even the author of this question stated: "Note that this question refferes to C# not necessarily .NET and how it handles the data under the hood (obviously it's all 1's and 0's.)"

Answer 16

Addressing the semantics, Why overload the word "object" so that it means "reference type" when we already have a perfectly good, unambiguous term for that -> "Reference Type", and the when, by overloading the word "Object" in this way we create the confusion this thread demonstrates... i.e., the mismatch between the fact that all Types, (including value types), inherit the implementation defined in the Type "System.Object". Clearly, this is at best unnecessary, and at worst extremely confusing.. Even the fact that the MS documentation is at times confusing on this issue is no excuse to propagate the confusion.

Much easier, and clearer, is to just define and use the term "object" to mean an instance of ANY type, value or reference, and the phrase "Reference Type" to describe the Types that use pointer variables and have their state stored on the Heap ...

Answer 17

A little late to the party, but I came across this in a search result on SO and figured the link below would help future generations:

Eric Lippert discusses this very thoroughly, with a much better (qualified) statement:

The way to correct this myth is to simply replace "derives from" with "is convertible to", and to ignore pointer types: every non-pointer type in C# is convertible to object.

The gist of it, if you hate reading well-illustrated explanations from people that write programming languages, is that (pointers aside), things like Interface, or generic parameter type declarations ("T") are not objects, but are guaranteed to be treatable as objects at runtime, because they have a definite instance, that will be an Object. Other types (Type, Enum, Delegate, classes, etc.) are all Objects. Including value types, which can be boxed to object as other answers have discussed.