

SF.22:为所有内部/非输出实体使用非命名(无名)命名空间
Nothing external can depend on an entity in a nested unnamed namespace. Consider putting every definition in an implementation source file in an unnamed namespace unless that is defining an "external/exported" entity.
任何外部实体都无法依赖位于嵌套无名命名空间内部的实体。考虑将所有实现源文件中的定义放入一个无名命名空间,除非它已经被定义为"external/exported"实体。
Example(示例)
An API class and its members can't live in an unnamed namespace; but any "helper" class or function that is defined in an implementation source file should be at an unnamed namespace scope.
API类和它的成员无法存在于无名命名空间中;但是任何定义在实现源文件中的"辅助"类或函数应该处于无名命名空间作用域中。
???原文链接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#sf22-use-an-unnamed-anonymous-namespace-for-all-internalnon-exported-entities