Difference between Object, Dynamic and Var

Question

I need to know the difference between these three keywords Object , Dynamic and var in C#.

I have seen this link but i don't understand in which case i have to use each one.

Can you explain for me, please, the difference between these keywords ? What are the utilities of each keyword?

Answer 1

Everything is Object because it is a base type for every type in .net environment. Every type inherit from Object in a moment, a simple int variable can be boxed to an object and unboxed as well. For example:

object a = 10; // int
object b = new Customer(); // customer object
object c = new Product(); // product object
object d = "Jon"; // string
object e = new { Name = "Felipe", Age = 20 }; // anonymous type

It is the most abstraction for any type and it is a reference type. If you want to get the real type, you need to unbox it (using a conversaion strategy such as methods, casts, etc):

object a = "Some Text";
string text = a.ToString();

// call a string method
text = text.ToUpper();

object i = 10; // declared as object but instance of int
int intValue = (int) i; //declare as an int ... typed

Dynamic is an implementation of a dynamic aspect in C#, it is not strongly typed. For example:

dynamic a = new Class();
a.Age = 18;
a.Name = "Jon";
a.Product = new Product();

string name  a.Name; // read a string
int age = a.Age; // read an int
string productName = a.Product.Name; // read a property
a.Product.MoveStock(-1); // call a method from Product property.

var is just a keyword of the C# language that allows you define any object of a type since you initialize it with a value and it will determinate the type from this value, for example:

var a = 10; // int
var b = 10d; // double
var c = "text"; // string
var d = 10m; // decimal
var p = new Product(); // Product type

The compiler will check the type of the value you have defined and set it on the object.