ref class中，如果不是为了编写组件跨越ABI，提供给其他语言使用，就使用internal。

详细资料

A ref class can contain public, protected, and private function members; only public and protected members are emitted into metadata.

A ref class can have standard C++ types in any private, internal, or protected private members.

Public ref classes that have type parameters are not permitted. User-defined generic ref classes are not permitted. A private, internal, or protected private ref class may be a template.

http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh699870.aspx