76. Everything is an object

Delving into the realm of object oriented programming, one phrase you may encounter is:

Everything is an object.

The degree to which this statement holds true is often used by enthusiasts to gauge the ‘purity’ of an object oriented language. This ‘purity’ does not refer to referential transparency but denotes the extent to which the language embodies the concept of an object. Is everything in the language an object?

For C#, a more accurate phrasing might be:

All values that can be constructed, and referenced using variables are or can be converted into objects.

This implies that in C#, almost every construct that holds a value, is, in essence, an object.

In C#, this idea stems from the fact that almost all types either, directly or indirectly, implicitly derive from the universal base class Object (whose alias is object) or can be converted to an object. Let’s illustrate the first case with an example:

class Cat {}

Object myObject = new Cat(); // An instance of a class can be upcast to 'Object'.

The below script needs to be able to find the current output cell; this is an easy method to get it.

Objects of an arbitrary class that we define ourselves, like the class Cat above can be upcast into the type Object. Generally, any instance of any class can be upcast to ‘Object’.

This is because, in C#, the universal baseclass of all classes is the class Object. Practically, think of it like this: whenever you don’t specify that a class inherits from some other class, then that class implicitly inherits from Object.

C# further extends this idea of “object-ness” to built-in value types like int, bool, and others, which can also be treated as objects. This is facilitated by a mechanism known as boxing, where value types are wrapped inside an object, allowing them to participate in object oriented behaviors.

int x = 7;

Object o = x; // Value types can be implicitly converted to 'Object'.

So while you strictly wouldn’t say that simple types are objects we could say that they can be implicitly converted into objects. Which for all intents and purposes means that we can think of them as being objects.

Note

In some languages, like Smalltalk or Ruby, even classes themselves are objects. In C#, the instances of a class are objects, not the class itself. If we, in regards to C#, say that a class is an object then we mean it in the sense of a cat being an animal. Meaning that the class is a subtype of Object.

This makes C# an almost purely object oriented language, with the caveat being a few non-object types, namely: pointers, interfaces, and open type parameters.

Pointers is an archaic feature borrowed from procedural languages and are not relevant to our object oriented perspective.

Although Interfaces are not objects themselves, any type that implements an interface by definition is an Object, since only classes can implement interfaces in C#. As a result, an instance of a class that implements an interface can be treated as an object of that interface type.

Open type parameters are central to generic programming in C# which we will talk about later. These are placeholder types replaced by concrete types (which are objects) during code execution.

So while C# indeed is a multi-paradigm language, incorporating principles of procedural, object oriented, and functional programming, it nevertheless strongly leans towards the object oriented side, treating almost all its types as objects.