c++ - 私有(private) typedef 的公共(public)使用是否可移植？

Question

class Settings
{
private:
    typedef std::map<std::string, SettingsOption> OptionMap;

public:
    typedef OptionMap::iterator iterator;
    typedef OptionMap::const_iterator const_iterator;

    ...
};

此代码可移植吗？关于它的标准规定是什么？

Answer 1

这是合法的，并且 Settings::iterator 和 Settings::const_iterator 可供 Settings 类的所有用户访问。

C++ 中的访问控制纯粹应用于名称。 ISO/IEC 14882:2011 11 [class.access]/4 中有一个注释和示例清楚地表明这是意图。

[...] [ Note: Because access control applies to names, if access control is applied to a typedef name, only the accessibility of the typedef name itself is considered. The accessibility of the entity referred to by the typedef is not considered. For example,

class A {
  class B { };
public:
  typedef B BB;
};

void f() {
  A::BB x; // OK, typedef name A::BB is public
  A::B y; // access error, A::B is private
}

—end note ]