Make U macro less problematic #1214

nickaein · 2019-07-31T13:56:43Z

I was getting compiler errors on ranges-v3 library when I included headers of this library. After wasting hours and almost giving up on this library, I found out that U macro is causing the issue and I can disable it by _TURN_OFF_PLATFORM_STRING macro.

Since this has caused several issues (#812, #473, #435), we can take some actions to mitigate future problems:

1. Make the documentation more visible

The current documentation on this macro is obscure. I even skimmed through FAQ but didn't notice it at the end of paragraph:

If you are using a library causing conflicts with the 'U' macro, for example Boost.Iostreams it can be turned off by defining the macro '_TURN_OFF_PLATFORM_STRING' before including the C++ REST SDK header files.

Mentioning this macro in homepage or usage section can increase its visibility and prevent possible mistakes.

2. Rename it. Having it is undefined behavior

Based on C++ Standard, identifiers with an underscore followed by an uppercase letter are reserved and defining them would be undefined behavior. Having this is not a good practice in such a well-known library.

3. Deprecate and eventually remove U

We can deprecate U and replace it with a more sensible macro definition. For keeping backward compatibility, we can have another macro (off by default) that when defined it brings back U for the users that heavily depends on it.

As reference (and helping the search engines), here is the compile errors I was getting:

ranges v-3: 0.4.0-1

Scanning dependencies of target nazdikpt
[  7%] Building CXX object CMakeFiles/nazdikpt.dir/src/server-db-logging.cpp.o
[  7%] Building CXX object CMakeFiles/nazdikpt.dir/src/application.cpp.o
[ 14%] Building CXX object CMakeFiles/nazdikpt.dir/src/server-http.cpp.o
[ 14%] Building CXX object CMakeFiles/nazdikpt.dir/src/server.cpp.o
In file included from /usr/include/range/v3/utility/concepts.hpp:26,
                 from /usr/include/range/v3/utility/copy.hpp:18,
                 from /usr/include/range/v3/begin_end.hpp:23,
                 from /usr/include/range/v3/core.hpp:17,
                 from /usr/include/range/v3/all.hpp:17,
                 from /home/isaac/balad-pt/include/map_matching.hpp:23,
                 from /home/isaac/balad-pt/include/bus_model.h:8,
                 from /home/isaac/balad-pt/include/transport_system.h:15,
                 from /home/isaac/balad-pt/include/application.h:3,
                 from /home/isaac/balad-pt/include/server.h:4,
                 from /home/isaac/balad-pt/src/server-db-logging.cpp:1:
/usr/include/range/v3/utility/swap.hpp:132:55: error: lambda-expression in template-argument
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                       ^
/usr/include/range/v3/utility/swap.hpp:132:56: error: capture of non-variable ‘N’
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                        ^
/usr/include/range/v3/utility/swap.hpp:129:50: note: ‘long unsigned int N’ declared here
                 template<typename T, typename U, std::size_t N>
                                                  ^~~
/usr/include/range/v3/utility/swap.hpp:132:58: error: template argument 2 is invalid
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                          ^
In file included from /usr/include/cpprest/asyncrt_utils.h:16,
                 from /usr/include/cpprest/http_msg.h:15,
                 from /usr/include/cpprest/http_listener.h:16,
                 from /home/isaac/balad-pt/include/server-http.h:7,
                 from /home/isaac/balad-pt/include/server.h:3,
                 from /home/isaac/balad-pt/src/server-db-logging.cpp:1:
/usr/include/range/v3/utility/swap.hpp:134:39: error: expected identifier before ‘&’ token
                 operator()(T (&t)[N], U (&u)[N]) const
                                       ^
In file included from /usr/include/range/v3/utility/concepts.hpp:26,
                 from /usr/include/range/v3/utility/copy.hpp:18,
                 from /usr/include/range/v3/begin_end.hpp:23,
                 from /usr/include/range/v3/core.hpp:17,
                 from /usr/include/range/v3/all.hpp:17,
                 from /home/isaac/balad-pt/include/map_matching.hpp:23,
                 from /home/isaac/balad-pt/include/bus_model.h:8,
                 from /home/isaac/balad-pt/include/transport_system.h:15,
                 from /home/isaac/balad-pt/include/application.h:3,
                 from /home/isaac/balad-pt/include/server.h:4,
                 from /home/isaac/balad-pt/src/server-db-logging.cpp:1:
/usr/include/range/v3/utility/swap.hpp:134:47: error: declaration of ‘u’ as array of references
                 operator()(T (&t)[N], U (&u)[N]) const
                                               ^
In file included from /usr/include/range/v3/utility/concepts.hpp:26,
                 from /usr/include/range/v3/utility/copy.hpp:18,
                 from /usr/include/range/v3/begin_end.hpp:23,
                 from /usr/include/range/v3/core.hpp:17,
                 from /usr/include/range/v3/all.hpp:17,
                 from /home/isaac/balad-pt/include/map_matching.hpp:23,
                 from /home/isaac/balad-pt/include/bus_model.h:8,
                 from /home/isaac/balad-pt/include/transport_system.h:15,
                 from /home/isaac/balad-pt/include/application.h:3,
                 from /home/isaac/balad-pt/include/server.h:4,
                 from /home/isaac/balad-pt/src/server.cpp:1:
/usr/include/range/v3/utility/swap.hpp:132:55: error: lambda-expression in template-argument
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                       ^
/usr/include/range/v3/utility/swap.hpp:132:56: error: capture of non-variable ‘N’
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                        ^
/usr/include/range/v3/utility/swap.hpp:129:50: note: ‘long unsigned int N’ declared here
                 template<typename T, typename U, std::size_t N>
                                                  ^~~
/usr/include/range/v3/utility/swap.hpp:132:58: error: template argument 2 is invalid
                     !is_adl_swappable_<T (&)[N], U (&)[N]>::value &&
                                                          ^
In file included from /usr/include/cpprest/asyncrt_utils.h:16,
                 from /usr/include/cpprest/http_msg.h:15,
                 from /usr/include/cpprest/http_listener.h:16,
                 from /home/isaac/balad-pt/include/server-http.h:7,
                 from /home/isaac/balad-pt/include/server.h:3,
                 from /home/isaac/balad-pt/src/server.cpp:1:
/usr/include/range/v3/utility/swap.hpp:134:39: error: expected identifier before ‘&’ token
                 operator()(T (&t)[N], U (&u)[N]) const
                                       ^
In file included from /usr/include/range/v3/utility/concepts.hpp:26,
                 from /usr/include/range/v3/utility/copy.hpp:18,
                 from /usr/include/range/v3/begin_end.hpp:23,
                 from /usr/include/range/v3/core.hpp:17,
                 from /usr/include/range/v3/all.hpp:17,
                 from /home/isaac/balad-pt/include/map_matching.hpp:23,
                 from /home/isaac/balad-pt/include/bus_model.h:8,
                 from /home/isaac/balad-pt/include/transport_system.h:15,
                 from /home/isaac/balad-pt/include/application.h:3,
                 from /home/isaac/balad-pt/include/server.h:4,
                 from /home/isaac/balad-pt/src/server.cpp:1:
/usr/include/range/v3/utility/swap.hpp:134:47: error: declaration of ‘u’ as array of references
                 operator()(T (&t)[N], U (&u)[N]) const
                                               ^
/usr/include/range/v3/utility/swap.hpp: In member function ‘constexpr meta::v1::if_c<(<expression error> && ranges::v3::is_swappable_with<T&, U&>::value)> ranges::v3::adl_swap_detail::swap_fn::operator()(...) const’:
/usr/include/range/v3/utility/swap.hpp:138:33: error: ‘t’ was not declared in this scope
                         (*this)(t[i], u[i]);
                                 ^
/usr/include/range/v3/utility/swap.hpp: In member function ‘constexpr meta::v1::if_c<(<expression error> && ranges::v3::is_swappable_with<T&, U&>::value)> ranges::v3::adl_swap_detail::swap_fn::operator()(...) const’:
/usr/include/range/v3/utility/swap.hpp:138:33: error: ‘t’ was not declared in this scope
                         (*this)(t[i], u[i]);
                                 ^
/usr/include/range/v3/utility/swap.hpp:138:39: error: ‘u’ was not declared in this scope
                         (*this)(t[i], u[i]);
                                       ^
/usr/include/range/v3/utility/swap.hpp:138:39: error: ‘u’ was not declared in this scope
                         (*this)(t[i], u[i]);
                                       ^
In file included from /usr/include/cpprest/asyncrt_utils.h:16,
                 from /usr/include/cpprest/http_msg.h:15,
                 from /usr/include/cpprest/http_listener.h:16,
                 from /home/isaac/balad-pt/include/server-http.h:7,
                 from /home/isaac/balad-pt/include/server.h:3,
                 from /home/isaac/balad-pt/src/server.cpp:1:
/usr/include/range/v3/detail/variant.hpp: In member function ‘void ranges::v3::detail::construct_fn<N, Ts>::construct_(U&, meta::v1::index_sequence<Is ...>)’:
/usr/include/range/v3/detail/variant.hpp:380:53: error: expected type-specifier before ‘static_cast’
                     ::new((void*)std::addressof(u)) U(static_cast<Ts&&>(std::get<Is>(args_))...);
                                                     ^
In file included from /usr/include/cpprest/asyncrt_utils.h:16,
                 from /usr/include/cpprest/http_msg.h:15,
                 from /usr/include/cpprest/http_listener.h:16,
                 from /home/isaac/balad-pt/include/server-http.h:7,
                 from /home/isaac/balad-pt/include/server.h:3,
                 from /home/isaac/balad-pt/src/server-db-logging.cpp:1:
/usr/include/range/v3/detail/variant.hpp: In member function ‘void ranges::v3::detail::construct_fn<N, Ts>::construct_(U&, meta::v1::index_sequence<Is ...>)’:
/usr/include/range/v3/detail/variant.hpp:380:53: error: expected type-specifier before ‘static_cast’
                     ::new((void*)std::addressof(u)) U(static_cast<Ts&&>(std::get<Is>(args_))...);
                                                     ^
make[2]: *** [CMakeFiles/nazdikpt.dir/build.make:297: CMakeFiles/nazdikpt.dir/src/server-db-logging.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: *** [CMakeFiles/nazdikpt.dir/build.make:323: CMakeFiles/nazdikpt.dir/src/server.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:73: CMakeFiles/nazdikpt.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

elfring · 2019-08-02T15:42:11Z

microsoft / cpprestsdk

Make U macro less problematic #1214

Make U macro less problematic #1214

nickaein commented Jul 31, 2019

elfring commented Aug 2, 2019

david-antiteum commented Jul 11, 2020

microsoft / cpprestsdk

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Make U macro less problematic #1214

Make U macro less problematic #1214

Comments

nickaein commented Jul 31, 2019

elfring commented Aug 2, 2019

david-antiteum commented Jul 11, 2020

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