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Monday, 15 December 2014

Difference between var and dynamic in C#

Table of difference



var
dynamic
Introduced inC# 3.0
Introduced inC# 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.
Needto initialize at the time of declaration.
e.g.,var str=”I am a string”;
Looking at the value assigned to the variablestr, the compiler will treat the variablestras string.
Noneedto 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 intellisensesince the type of variable assigned is known to compiler.
Intellisense is not availablesince the type and its related methods and properties can be known at run time only


e.g.,var obj1;
willthrow a compile errorsince 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.var obj1=1;
will compile
var obj1=” I am a string”;
will throw errorsince 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.dynamic obj1=1;
will compile and run
dynamic obj1=” I am a string”;
will compile and runsince 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.

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