01_compiles.c++

    // ...

    inline std::vector<benchmark>& benchmark_registry() {
        static std::vector<benchmark> registry;
        return registry;
    }

    struct benchmark_registrar {
        template <typename Fun>
        benchmark_registrar(std::string name, Fun&& registrant) {
            benchmark_registry().emplace_back(std::move(name), std::forward<Fun>(registrant));
        }
    };
} // namespace nonius

#define NONIUS_BENCHMARK(name, ...) \
    namespace { static ::nonius::benchmark_registrar NONIUS_DETAIL_UNIQUE_NAME(benchmark_registrar) (name, __VA_ARGS__); }

02_does_not_compile.c++

    // ...

    inline std::vector<benchmark>& benchmark_registry() {
        static std::vector<benchmark> registry;
        return registry;
    }

    struct benchmark_registrar {
        template <typename Fun>
        benchmark_registrar(std::vector<benchmark>& registry, std::string name, Fun&& registrant) {
            registry.emplace_back(std::move(name), std::forward<Fun>(registrant));
        }
    };
} // namespace nonius

#define NONIUS_BENCHMARK(name, ...) \
    namespace { static ::nonius::benchmark_registrar NONIUS_DETAIL_UNIQUE_NAME(benchmark_registrar) (::nonius::benchmark_registry(), name, __VA_ARGS__); }