Difference Between "Var" and "Object" in C#

Difference between Object, Dynamic and Var

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.

var vs Object in C#

var is just shorthand for "let the compiler pick the right variable type for me" (compile-time type-inference is the more exact term).

object, on the other hand, is a specific type; all other reference types derive from object, so you can assign anything to a variable of type object.

Difference between variable and object

Creating a variable has 2 parts, Declaration and Assignment.

In the Declaration part, you state that the variable exists and you state its type:

DataRow dr; // Create's a variable of type DataRow with a value of null.

The Assignment takes a value and point the variable to it:

dr = new DataRow(); // Creates a new DataRow and points dr variable to it.

You can do them both in the same line like that:

DataRow dr = new DataRow();

The result is the same as if you would separate those into the 2 lines above and the type of the variable is in both cases DataRow.

The object inside the variable however can be of an inherited type:

class MyDataRow : DataRow
{
}

DataRow dr = new MyDataRow(); //Creates a new object of type MyDataRow and points dr to it.

Managed objects must be held by a variable otherwise they are Garbage Collected.

Difference between var and object in C#

Beginning in Visual C# 3.0, variables that are declared at method scope can have an implicit type var. An implicitly typed local variable is strongly typed just as if you had declared the type yourself, but the compiler determines the type. The following two declarations of i are functionally equivalent:

var i = 10; //implicitly typed
int i = 10; //explicitly typed

var isn't object

You should definitely read this : C# 3.0 - Var Isn't Object

Difference between Dynamic, Var and Object

Here is some differences. Hope this will help to you.

Difference between Var type and object type in C#

Both are compiled to the same MSIL code. The only difference is a possible convenience for you while writing source code - if you decide to change the type of p later on, you only have to replace Person once in the constructor call and you can leave the variable declaration intact when using var.

That said, var goes along with a slight decrease in legibility, as you cannot see the type of p instantly any more at the beginning of your line. Therefore, restrict your use of var to occasions where it really saves some typing, such as for complicated nested generic types.

Note that, if you do not initialize your variable right away (in the same statement where the variable is declared), you cannot use var as the compiler cannot infer the type of the variable.

Difference between var and Class class in object creation

When declaring a variable with the var keyword, the compiler infers the type of the variable from the right-hand side of the assignment. In particular, it uses the type the expression on the right-hand side of the assignment operator (=) evaluates to.

Therefore, for your declaration

var c = new C();

, the variable c will be declared as type C.

If you want c to have any other type, there are basically two options:

• Either indicate the type of c explicitly: B c = new C();
• Alternatively, you can change your right-hand side expression to be recognized as the type of choice: var c = (B)(new C());

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As for your more detailed questions:

• B c = new C() creates an instance of type C. That is what new C() does. The fact that variable c is typed to B only means that the compiler will assume that c has any properties and methods of type B, but not necessarily of type C. Likewise, you are allowed to assign not only instances of type C, but also instances of type B to c at a later time.
• Indeed, you can use this style when you are not sure whether c will at some point reference an instance of type B, rather than exclusively instances of type C.

What is the difference between var a = new className() {id = , Name = } and var a = new className {id=,Name=}}

Calling new className opposed to new className() will make no difference. They both call the default constructor. The spacing difference is irrelevant too.

Both code segments are rewritten by the compiler to something equivalent to:

className a = new className();
a.id = "foo";
a.Name = "sass";

Using listtype or var keyword difference

They are the same. var is implicitly typed.

If you hover over the keyword var in Visual Studio, it will show you the type of your object - in this case List<string>. The use of var is only to clean up code - you already know you're creating an object of type List<string>, so some people think it is redundant to type:

List<string> list = new List<string>();

There is no performance difference, as the compiler already knows what type the object is. Using var personal preference mostly - you can use it if you want to and there is no performance hit.

Eric Lippert has a great blog post about var here.

I think you're confusing var and dynamic, which are two totally different things. The dynamic type is a type that allows you to assign values of different types to it at runtime.

What's the difference between dynamic (C# 4) and var?

var is static typed - the compiler and runtime know the type - they just save you some typing... the following are 100% identical:

var s = "abc";
Console.WriteLine(s.Length);

and

string s = "abc";
Console.WriteLine(s.Length);

All that happened was that the compiler figured out that s must be a string (from the initializer). In both cases, it knows (in the IL) that s.Length means the (instance) string.Length property.

dynamic is a very different beast; it is most similar to object, but with dynamic dispatch:

dynamic s = "abc";
Console.WriteLine(s.Length);

Here, s is typed as dynamic. It doesn't know about string.Length, because it doesn't know anything about s at compile time. For example, the following would compile (but not run) too:

dynamic s = "abc";
Console.WriteLine(s.FlibbleBananaSnowball);

At runtime (only), it would check for the FlibbleBananaSnowball property - fail to find it, and explode in a shower of sparks.

With dynamic, properties / methods / operators / etc are resolved at runtime, based on the actual object. Very handy for talking to COM (which can have runtime-only properties), the DLR, or other dynamic systems, like javascript.

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