What's the difference between dynamic and var keyword?

Many folks have expressed misunderstanding around the difference between var and dynamic in C#.  For both of them, the type is inferred rather than explicitly declared. 

dynamic test = 1;

var test2 = 2;

If I hover my mouse over the “var” in the code above, IntelliSense will show me that the compiler has correctly inferred that it is an Int32.  If I hover over “dynamic”, it will continue to be typed as “dynamic” since dynamic types aren’t resolved until runtime. 

However, var is statically typed, and dynamic is not. 

// Can a dynamic change type? 

dynamic test = 1;

test = "i'm a string now";  // compiles and runs just fine

var test2 = 2;

test2 = "i'm a string now"; // will give compile error

This is one of the key differences between dynamic and var.  A var is an implicitly typed variable that is inferred by the compiler, but it is just as strongly typed as if you had explicitly typed it yourself using “int test2 = 2;”.  A dynamic variable bypasses all compile-time type checking and resolves everything at runtime, which generates the following scenario.

dynamic test = "i'm a string now"; 

Console.WriteLine(test.Alpha); // Won’t prompt any error as property will be checked at

runtime, resulting in exception

Other big difference between dynamic and var keyword, “dynamic” can be set as function return type while “var” cannot.

public dynamic dfunc()// Will be compiled successfully

{

    return "";

}

public var func()//Compile time error

{

    return "";

}