c++ - 是否可以在 C++ 中创建可重新定义的命名空间别名？

Question

我想创建一个命名空间别名，该别名可以全局更改以在运行时引用不同的范围。考虑一下:

#include <iostream>

namespace scopePrimary {
    int somethingOfInterest = 1;
}
namespace scopeSecondary {
    int somethingOfInterest = 2;
}
namespace scopeTarget = scopePrimary;

int doStuffInTargetScope() {
    using namespace scopeTarget;
    return somethingOfInterest;
}

int main() {
    // Do something with the somethingOfInterest variable defined in scopePrimary
    std::cout << "doStuffInTargetScope():\n" \
    "  somethingOfInterest = " << doStuffInTargetScope() << std::endl;

    namespace scopeTarget = scopeSecondary;
    using namespace scopeTarget;

    // Do something with the somethingOfInterest variable defined in scopeSecondary
    std::cout << "doStuffInTargetScope():\n" \
    "  somethingOfInterest = " << doStuffInTargetScope() << std::endl;

    std::cout << "main():\n  somethingOfInterest = "
    << somethingOfInterest << std::endl;
}

现在，上面的代码确实可以编译，但不是我期望的输出:

doStuffInTargetScope():
  somethingOfInterest = 1
doStuffInTargetScope():
  somethingOfInterest = 2
main():
  somethingOfInterest = 2

我得到这个输出:

doStuffInTargetScope():
  somethingOfInterest = 1
doStuffInTargetScope():
  somethingOfInterest = 1
main():
  somethingOfInterest = 2

似乎在尝试重新定义 namespace scopeTarget 时, C++ 只会使用最局部的别名定义，而不是覆盖全局别名。
有没有人知道在这里实现我的目标的解决方法？

Answer 1

您不能在运行时更改 namespace 。函数指针会达到预期的效果。

有关命名空间，请参阅:Renaming namespaces

对于函数指针，我发现这很有用:https://www.learncpp.com/cpp-tutorial/78-function-pointers/