c++ - 为什么允许 std::atomic_{char,schar,etc.} typedef 是 std::atomic 基类的类型定义，而不仅仅是 atomic？

Question

C++11 [atomics.types.generic]p7:

There shall be named types corresponding to the integral specializations of atomic, as specified in Table 145, and a named type atomic_bool corresponding to the specified atomic<bool>. Each named type is a either typedef to the corresponding specialization or a base class of the corresponding specialization. If it is a base class, it shall support the same member functions as the corresponding specialization.

(强调)

让std::atomic_char的理由是什么？不等于 std::atomic<char> ，等等所有其他类型？这带来了什么样的灵 active ，为什么有用？乍一看，我不明白为什么不需要将这些类型定义为 std::atomic<T>直接特化。

请注意 N2427哪个提议<atomic>说 typedef 完全是专门化的，而不可能是基类。

Answer 1

它可能存在，因为有人已经使用 std::atomic_* 类型作为基类实现了原子，并且对这种方法提示很多/提供了一个很好的论据。

在MSVC建议这样的实现。

在this据称

Remove the definional base-class relationship between atomic_.... named types and the corresponding specializations of the atomic template class. The base-class relationship is now implementation-dependent. This change ensures compatibility with C. Some member functions and operators, that were formerly inherited from the base class, must be hoisted from the named types to the specializations.