C++

13.8    “inline namespace”

The last way to define a namespace is together with inline. You create an inline namespace as in the following listing.

// https://godbolt.org/z/115M1csEE#include <iostream>namespace mylib {    namespace v1 {        int version() { return 1; }    }    inline namespace v2 { // current version        int version() { return 2; }    }}int main() {    std::cout << "Version " << mylib::version() << "\n";     // Output: 2    std::cout << "Version " << mylib::v1::version() << "\n"; // Output: 1    std::cout << "Version " << mylib::v2::version() << "\n"; // Output: 2}  

Listing 13.7     The identifiers of an inline namespace also go into its surrounding namespace.

With the inline before namespace, you open a normal namespace. In addition, all identifiers are also ...