Difference Between Var and Dynamic keywords & A small story. :)

 

Var Dynamic
1. The var keyword was introduced in .net 3.0 framework The Dynamic keyword was introduced in .net 4.0 framework
2. var is used to declare a variable, its data type is determined at the time of its declaration that means it is decided at compile time. Dynamic is also used to declare a variable, however its data type is not determined at the time of its declaration that means it is decided at run time.
3. You cannot change its type at run time. You can change its type at run time.
4. For e.g. if you declare a variable and assign a value(i.e. var variable1 = 1;)in that case compiler will considered it as integer and at run time if u change its value to string, an error will be thrown conversion from string to integer is failed. For e.g. if you declare a variable and assign a value (i.e. Dynamic variable1 = 1;) in that case compiler will not determine its type and run time you can change its value from string to integer.
5. The advantage of var :  if u assign any value from any  objects or variables to var, you will not have to decide its type explicitly, the compiler will set its data type based on assigned value and hence it useful for linq The advantage dynamic :  since value can be assigned at run time you can changes its data type by assigning value of type objects or variables at run time.
6. One more thing about var to remember is, var cannot be declared at class level and also it cannot be used as return type for any function. However dynamic can be declared at class level and also it can be used as return type for any function.
7.  Any invalid operation is caught at compile time.E.g. 

public class ClsStudent
{
Public void FunPubStd1()
{}
}
var  ObjLocClsStudent = new ClsStudent();
ObjLocClsStudent. FunPubStd1()
ObjLocClsStudent. FunPubStd2()

In above mentioned example compiler will throw an error since it will not get function FunPubStd2 while compilation.

Any invalid operation is caught at run timeE.g. 

public class ClsStudent
{
Public void FunPubStd1()
{}
}
var  ObjLocClsStudent = new ClsStudent();
ObjLocClsStudent. FunPubStd1()
ObjLocClsStudent. FunPubStd2()

In above mentioned example compiler will not throw an error since it will not check at run time.

 

 

Let’s take one real life example to differentiate between var and dynamic type and also use of one over another.

E.g. let’s imagine we are going to market to buy some vegetables and for that we are carrying a small polythene container however we get a call from home to bring 10 litters oil as well. Now problem arises here, how to carry 10 litters oil since we don’t have big tin container to carry a huge quantity of oil. You know why this problem raised because while leaving home we were asked to bring vegetables only so we carried only small polythene container and latter we were asked to bring oil only which is not possible to carry in small polythene container. So now just think if we would have such kind of container which is used to carry anything from small to large solid and liquid item well.

The same problem may arise in coding also as while compile time we might not know which types of data needs to be stored or carried So to overcome this problem we have dynamic type which can be used where compile time we don’t know the type of data we are going to get.  

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By Sriramjithendra Posted in C#.NET

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