Modifiers in C#

Modifiers are used to modify declarations of types and type members. Following are the modifiers comes in C# (MSDN)

sealed #

• In classes, sealed modifier prevents other classes from inheriting from it.
• Can also use sealed modifier on a method or property that overrides a virtual method or property in a base class
• Enables you to allow classes to derive from your class and prevent them overriding specific virtual methods or properties 

• When applied to a method or property sealed must always used with override 
• Structs are implicitly sealed, they cannot be inherited. This is because structs are value types 

virtual #

• Virtual is used to modify methods, properties, indexers or event declarations and to be overriden in a derived class. 
• virtual member can be changed in a derived class with override modifier. 
• By default methods are non-virtual. Therefore you cannot override a non-virtual method. 
• Virtual members are an implementation of type-based polymorphism. When you have a base class and a derived class, the derived class can re-implement the base class virtual method thus giving you dynamic entry point to the class type.
• You cannot create private virtual members. You'll get virtual or private members cannot be private Exception.
• virtual properties behave like abstract methods, with few differences.

http://www.dotnetperls.com/virtual

abstract #

• indicates thing being modified has a missing or incomplete implementation
• abstract method is implicitly virtual

default (SO)

• For a reference type returns null
• For a value type other than Nullable<T> returns 0 initialized value
• For Nullable<T> returns empty value

const 

- Cannot change (compile time constants)

- http://stackoverflow.com/questions/555534/when-if-ever-should-we-use-const

readonly

- Can change in the constructors. (runtime constants)

• async
• event
• extern
• new
• override
• partial
• static
• unsafe
• volatile