Instances and variables in C#

Question

In C# when you create a variable you create a value of a certain type, for example a bool can only receive true or false, one int whole numbers and so on and so forth...

I wanted to know how these values would be classified, true, false, 2, 2.5f...

They can be classified as instances or objects?

An instance is a value that is a copy of the original value with some changes?

Answer 1

Yes, these described data are instances or objects, everything that is stored in memory during the execution is an instance of a type, is a concrete data based on some model that can be simple or complex, in these cases are very simple, are data that the processor recognizes, but they all occupy memory space. Even a true (that in the background is a stored number 1) is an instance.

If this is not an instance, then what? Why would it be different? Always keep in mind what I have answered in previous question that objects are just the concreteness of a model, no matter what this model is, it can be a very simple number of 1 byte or a few bytes that the processor understands, or something more complex that involves several parts.

And instances need not even be associated with variables, values can exist and, of course, be stored in memory without having a name linked to this memory address where the value is.

The instance is the object, and only this, has nothing copy, original value, change, none of that.

It is an instance, no matter if the type is by value or by reference. So these values are all objects (instances) equal to objects created based on classes, what changes is the form of access and eventually the place where the object is stored. See more in What’s the difference between Struct and Class?. Types by value usually (but not necessarily) are immutable and that means that any changes you try to make in it require you to create an instance. The reference types can be, in the case of string, but usually are not. Also: Memory allocation in C# - Value types and reference types.

It may also be useful to see How a "struct" is organized in memory?. These types that are exemplified in the question are like structs.

var i = 1;

generates an instance of the type int (has 4 bytes, one of which is the signal) and their order depends on architecture) and it is stored in memory, in this case in the stack, because it is a local variable.

class Exemplo {
    private int i = 1;
}

It is now stored inside another object and will be stored in the heap since the object container is a class. At least so far, there are indications that in the future some classes may be allocated in the stack as optimization. In this case there is an instance of int which is within an instance of Exemplo when it is created at some point in the code. All classes and structures created with C# code are composed of one or more instances of some kind. So:

var e = new Exemplo();
Write(e.i); //acessando a instância de `i` dentro da instância `e`.

And yet we can place an instance of a int in the heap:

object i = 1;

In this case 1 is an integer value that will be stored inside an object of type object and that being a class will be in the heap. You cannot access this value without a cast because object does not know how to access a value, it should originally have no value. When you do the cast is only accessing the already created instance, it does not create, convert or change anything:

Write((int)i);

I put in the Github for future reference.

That’s a Unboxing, but is irrelevant to the question.

More:

• Where I must instantiate objects?
• What are and where are the "stack" and "heap"?
• What’s the difference in instantiating, initializing and declaring a variable?
• How a class is organized in memory?
• In programming, what is an object?
• Difference between primitive type and object in Java
• Concept of class, entity and objects