Expected primary-expression before decltype CROW_MIDDLEWARES

[Iuliean]

    template<unsigned N, const char(&url)[N], typename M, typename Func>
    void add_route (crow::HTTPMethod&& method, Func f)
    {
        this->app.route<crow::black_magic::get_parameter_tag(url)>(url)
            .CROW_MIDDLEWARES(this->app, M).methods(method)(f);
    }

The above mentioned code gives me these errors

In file included from ../dependencies/includes/Crow/include/crow.h:25,
                 from site.h:2,
                 from app.h:2,
                 from app.cpp:1:
site.h: In member function ‘void Site::add_route(crow::HTTPMethod&&, Func)’:
../dependencies/includes/Crow/include/crow/app.h:32:48: error: expected primary-expression before ‘decltype’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: note: in definition of macro ‘CROW_MIDDLEWARES’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: error: expected ‘;’ before ‘decltype’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: note: in definition of macro ‘CROW_MIDDLEWARES’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~

i am calling the function like this this->add_route<sizeof(str), str, Authentificator>(crow::HTTPMethod::GET, [](){return "lol";});
and authentificator is defined like this

struct Authentificator : crow::ILocalMiddleware
{
    struct context{};

    void before_handle()
    {
        CROW_LOG_DEBUG << "keek";
    }

    void after_handle()
    {
        CROW_LOG_DEBUG << "lol";
    }
};

[dranikpg]

Hi! Currently CROW_MIDDLEWARES has to be used in the last place 😓

.methods(method) .CROW_MIDDLEWARES(this->app, M)(f)

should do the job

[Iuliean]

i've tried that too and it doesnt work

  template<unsigned N, const char(&url)[N], typename M, typename Func>
    void add_route (crow::HTTPMethod&& method, Func f)
    {
        this->app.route<crow::black_magic::get_parameter_tag(url)>(url).methods(method)
            .CROW_MIDDLEWARES(this->app, M)(f);
    }

make[1]: Entering directory '/home/iulian/development/PiThermostatCPP/src'
arm-linux-gnueabihf-g++ -c -o /home/iulian/development/PiThermostatCPP/intermediates/release/app.o app.cpp -I../dependencies/includes/ -I../dependencies/includes/Crow/include/ -I../dependencies/includes/WiringPi/wiringPi/ -O3
In file included from ../dependencies/includes/Crow/include/crow.h:25,
                 from site.h:2,
                 from app.h:2,
                 from app.cpp:1:
site.h: In member function ‘void Site::add_route(crow::HTTPMethod&&, Func)’:
../dependencies/includes/Crow/include/crow/app.h:32:48: error: expected primary-expression before ‘decltype’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: note: in definition of macro ‘CROW_MIDDLEWARES’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: error: expected ‘;’ before ‘decltype’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~~~~~~
../dependencies/includes/Crow/include/crow/app.h:32:48: note: in definition of macro ‘CROW_MIDDLEWARES’
   32 | #define CROW_MIDDLEWARES(app, ...) middlewares<decltype(app), __VA_ARGS__>()
      |                                                ^~~~~~~~
make[1]: *** [Makefile:14: /home/iulian/development/PiThermostatCPP/intermediates/release/app.o] Error 1
make[1]: Leaving directory '/home/iulian/development/PiThermostatCPP/src'
make: *** [Makefile:45: thermostat] Error 2

[dranikpg]

This code should work (clang13 / g++11 both swallow it). Note the template before middlwares()

template<unsigned N, const char(&url)[N], typename M, typename Func>
void add_route(crow::HTTPMethod method, Func f) {
  app.route<crow::black_magic::get_parameter_tag(url)>(url)
    .methods(method)
    .template middlewares<decltype(app), M>()(f);
}

Unfortunately, Crow uses inconvenient constexpr char arrays for paths and the error becomes hard to decrypt 😀 . Now that your app.route() depends on your template arguments, .middlewares<> becomes a dependent template name and has to be prefixed with template.

Btw, looks a little less confusing with macros.

CROW_ROUTE(app, url)
    .methods(method)
    .template CROW_MIDDLEWARES(app, M)(f);

Hope that helps

[dranikpg]

I'll think about the implications of adding the template keyword to CROW_MIDDLEWARES. While it might technically be obsolete at times, it shouldn't break anything and would resolve such issues

[Iuliean]

yes that worked thanks for the help

[The-EDev]

Closing this issue as the initial problem was solved. See #369 for adding template to the macro.