C#:访问修饰符 Access Modifier

共有5个访问修饰符：public, private, protected, internal, protected internal

类本身有2道防线，一是命名空间（namespace)，另一个是程序集（Assembly)。

成员则有3道防线，一是类，另外两个同类一样。

而访问修饰符则是类或成员走向外界的一把钥匙。

类存在于命名空间之下，只能为 public 或 internal修饰，默认为internal

成员则可以有5个访问修饰符，但默认为private, 默认遵循最小权利原则

The accessibility of the member cannot be greater than the type.

User-defined operators must always be declared as public.

Interface members are always public because the purpose of an interface is to enable other types to access a class or struct. No access modifiers can be applied to interface members.

Enumeration members are always public, and no access modifiers can be applied.