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Difference Between var and dynamic in C#

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17 Jun 2013CPOL2 min read 375.3K   69   50
Difference between var and dynamic in C#

Introduction

The type keyword 'var' was introduced in C# 3.0 (.NET 3.5 with Visual Studio 2008) and the type 'dynamic' was introduced in C# 4.0 ( .NET 4.0 with Visual Studio 2010). Let us see the difference between these two.

Background

Variables declared with var are implicitly but statically typed. Variables declared with dynamic are dynamically typed. This capability was added to the CLR in order to support dynamic languages like Ruby and Python.

This means that dynamic declarations are resolved at run-time, var declarations are resolved at compile-time.

Table of Difference

var dynamic

Introduced in C# 3.0

Introduced in C# 4.0

Statically typed – This means the type of variable declared is decided by the compiler at compile time.

Dynamically typed - This means the type of variable declared is decided by the compiler at runtime time.

Need to initialize at the time of declaration.

e.g., var str=”I am a string”;

Looking at the value assigned to the variable str, the compiler will treat the variable str as string.

No need to initialize at the time of declaration.

e.g., dynamic str;

str=”I am a string”; //Works fine and compiles

str=2; //Works fine and compiles

Errors are caught at compile time.

Since the compiler knows about the type and the methods and properties of the type at the compile time itself

Errors are caught at runtime

Since the compiler comes to about the type and the methods and properties of the type at the run time.

Visual Studio shows intellisense since the type of variable assigned is known to compiler.

Intellisense is not available since the type and its related methods and properties can be known at run time only

 

e.g., var obj1;

will throw a compile error since the variable is not initialized. The compiler needs that this variable should be initialized so that it can infer a type from the value.

e.g., dynamic obj1;

will compile;

e.g. This code snippet of two statements -

{

var obj1=1;

obj1=”I am a string”;

}

will throw error since the compiler has already decided that the type of obj1 is System.Int32 when the value 1 was assigned to it. Now assigning a string value to it violates the type safety.

e.g. This code snippet of two statements -

{

dynamic obj1=1;

obj1=”I am a string”;

}

will compile and run since the compiler creates the type for obj1 as System.Int32 and then recreates the type as string when the value “I am a string” was assigned to it.

This code will work fine.

History

  • 17th September, 2012: Submitted the tip and trick

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
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Software developer by profession, working for a service and product based organisation in India.

Career graph:
Software Programmer since 2002.
Web Developer in ASP.NET since 2004.

Interests:
I love reading the blogs and articles of technology experts. I love codeproject and stackoverflow .

I love to share knowledge and help the programmers. I appreciate if some body corrects my code or my concepts which helps me learn.

Comments and Discussions

 
QuestionI voted 5 Pin
AnotherKen12-Jun-13 15:45
professionalAnotherKen12-Jun-13 15:45 
AnswerRe: I voted 5 Pin
bbirajdar12-Jun-13 21:10
bbirajdar12-Jun-13 21:10 
GeneralMy vote of 5 Pin
Paulo Morábito Neto12-Jun-13 6:50
professionalPaulo Morábito Neto12-Jun-13 6:50 
GeneralRe: My vote of 5 Pin
bbirajdar12-Jun-13 8:57
bbirajdar12-Jun-13 8:57 
GeneralGood Comparison Pin
Rajneesh Rai10-Jun-13 20:29
Rajneesh Rai10-Jun-13 20:29 
GeneralRe: Good Comparison Pin
bbirajdar12-Jun-13 8:58
bbirajdar12-Jun-13 8:58 
GeneralMy vote of 5 Pin
Renju Vinod29-May-13 0:05
professionalRenju Vinod29-May-13 0:05 
GeneralRe: My vote of 5 Pin
bbirajdar12-Jun-13 8:58
bbirajdar12-Jun-13 8:58 
Thank you
GeneralMy vote of 3 Pin
Thanasis I.17-Sep-12 11:03
Thanasis I.17-Sep-12 11:03 
QuestionNot exactly right Pin
Thanasis I.17-Sep-12 11:02
Thanasis I.17-Sep-12 11:02 
SuggestionMy vote of 3 Pin
HeWillem17-Sep-12 2:46
HeWillem17-Sep-12 2:46 
GeneralRe: My vote of 3 Pin
bbirajdar17-Sep-12 3:03
bbirajdar17-Sep-12 3:03 
AnswerRe: My vote of 3 Pin
Christian Amado17-Sep-12 3:15
professionalChristian Amado17-Sep-12 3:15 
GeneralRe: My vote of 3 Pin
Lev Pavlas17-Sep-12 7:06
Lev Pavlas17-Sep-12 7:06 
GeneralRe: My vote of 3 Pin
HeWillem26-Sep-12 4:40
HeWillem26-Sep-12 4:40 
GeneralRe: My vote of 3 Pin
bbirajdar26-Sep-12 5:38
bbirajdar26-Sep-12 5:38 
GeneralRe: My vote of 3 Pin
johannesnestler17-Jun-13 4:26
johannesnestler17-Jun-13 4:26 
GeneralMy vote of 5 Pin
Christian Amado17-Sep-12 2:23
professionalChristian Amado17-Sep-12 2:23 
GeneralRe: My vote of 5 Pin
bbirajdar17-Sep-12 3:04
bbirajdar17-Sep-12 3:04 

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