Inline namespaces are transparent for those who are using the outer namespace.
A simple example:
#include <iostream>
namespace m42e {
namespace cpp {
namespace test {
const int32_t my42 = 42;
inline namespace nested {
const int32_t my23 = 23;
} // namespace nested
} // namespace test
} // namespace cpp
} // namespace m42e
int main() {
// this works for sure
std::cout << m42e::cpp::test::my42 << std::endl;
std::cout << m42e::cpp::test::nested::my23 << std::endl;
{
using namespace m42e::cpp::test;
// of course we can use my42 here
std::cout << my42 << std::endl;
// as nested is inline it is "transparent"
std::cout << my23 << std::endl;
}
return 0;
}