c# 4.0 new features

Introduction

C# 4.0 includes following some great features.

Dynamic Types

C# 4.0 supports dynamic types. This functionality is most useful in dynamic languages that require runtime bindings. Using Dynamic types you can defer the type checking to Runtime

Optional Parameter

Using Optional Parameter, We can avoid creating many overloads of methods by specifying default values of some parameters.

Named Parameter

In C# 4.0, We can call the methods with named parameter

Simplify COM interop

In C# 4.0, We can simplify the COM interop operations using dynamic type and optional parameters..

Variance

Variance is the collective term for covariance and contravariance, two concepts that have been introduced in .NET 4.

From wikipedia:-
covariant - converting from wider (double) to narrower (float).
contravariant - converting from narrower (float) to wider (double)
invariant-Not able to convert

Manager _manager = New Manager();
Employee _employee = _manager;

Here, an object of type Manager has been placed into a variable of type Employee — which is possible because Manager derives from Employee.

IEnumerable<Manager> _managerList = New IEnumerable<Manager>();
IEnumerable<Employee> _employeeList = _managerList;