C# 5.0 Pocket Reference

Access Modifiers

To promote encapsulation, a type or type member may limit its accessibility to other types and other assemblies by adding one of five access modifiers to the declaration:

public

Fully accessible. This is the implicit accessibility for members of an enum or interface.

internal

Accessible only within the containing assembly or friend assemblies. This is the default accessibility for non-nested types.

private

Accessible only within the containing type. This is the default accessibility for members of a class or struct.

protected

Accessible only within the containing type or subclasses.

protected internal

The union of protected and internal accessibility (this is more permissive than protected or internal alone, in that it makes a member more accessible in two ways).

In the following example, Class2 is accessible from outside its assembly; Class1 is not:

class Class1 {}         // Class1 is internal (default)
public class Class2 {}

ClassB exposes field x to other types in the same assembly; ClassA does not:

class ClassA { int x;          }  // x is private
class ClassB { internal int x; }

When overriding a base class function, accessibility must be identical on the overridden function. The compiler prevents any inconsistent use of access modifiers—for example, a subclass itself can be less accessible than a base class, but not more.

Friend Assemblies

In advanced scenarios, you can expose internal members to other friend assemblies by adding the System.Runtime.CompilerServices.InternalsVisibleTo assembly ...