Re: [Libmesh-users] Suggestion: turn some macros into functions

[edgar <edg...@cr...>]

> Hi Edgar,
> 
> I don't think this mailing list --8<-- accept{s} attachments.

I live in a bubble :P .

> Second best would be to paste a diff into
> the body of an email (assuming it's not too long, in which case the 
> first
> option should be used).

Third best: create a fork on notabug.org or GNU Savannah and send you 
the link to the corresponding branch, right? ;D

In any case, below is the original suggestion. Let me know if you like 
the idea, and I will create the branch on notabug.org :D .

   Hello,

   I would kindly and respectfully like to suggest turning some macros in 
=libmesh_common.h= into functions. As I was exploring libMesh, I naïvely 
tried this:

   #+CAPTION: Using the =libmesh_error_msg= macro
   #+begin_src cpp :libs $(libmesh-config --cxxflags --include --ldflags 
--libs)
     #include <stdio.h>
     #include <iostream>
     #include "libmesh/libmesh.h"
     #include "libmesh/mesh.h"

     int main (int argc, char * argv[]){
       libMesh::LibMeshInit init(argc, argv);

       if (argc < 4){
         libMesh::libmesh_error_msg("Usage: ");
       }

     }
   #+end_src

   #+caption: Result from using =libmesh_error_msg= (does not compile).
   #+begin_example
     In file included from /usr/include/libmesh/libmesh.h:25,
                      from /tmp/babel-hlBzed/C-src-YQnbkN.cpp:3:
     /tmp/babel-hlBzed/C-src-YQnbkN.cpp: In function 'int main(int, 
char**)':
     /tmp/babel-hlBzed/C-src-YQnbkN.cpp:15:14: error: expected 
unqualified-id before 'do'
        15 |     libMesh::libmesh_error_msg("Usage: " // << argv[0] <<
           |              ^~~~~~~~~~~~~~~~~
   #+end_example

   This does not work, because =libmesh_error_msg= is actually a macro 
defined in =libmesh_common.h=, and does not need =libMesh::=.

   If, however, the macro is replaced with the code, it should produce:
   #+caption: Using the raw text from =libmesh_error_msg=
   #+begin_src cpp :libs $(libmesh-config --cxxflags --include --ldflags 
--libs)
     #include <stdio.h>
     #include <iostream>
     #include "libmesh/libmesh.h"
     #include "libmesh/mesh.h"

     int main (int argc, char * argv[]){
       libMesh::LibMeshInit init(argc, argv);

       if (argc < 4){
         char msg[] = "Usage: ";
         do {
           libMesh::err << msg << std::endl;
           std::stringstream msg_stream;
           msg_stream << msg;
           libMesh::MacroFunctions::report_error(__FILE__, __LINE__, 
LIBMESH_DATE, LIBMESH_TIME);
           LIBMESH_THROW(libMesh::LogicError(msg_stream.str()));
         } while (0);
       }

     }
   #+end_src

   #+caption: Expected output (error message from libMesh) with raw text 
from =libmesh_error_msg=
   #+begin_example
     Usage:
     Stack frames: 5
     0: libMesh::print_trace(std::ostream&)
     1: libMesh::MacroFunctions::report_error(char const*, int, char 
const*, char const*)
     2: /tmp/babel-hlBzed/C-bin-tb49Ls(+0xcdee) [0x563818bc5dee]
     3: __libc_start_main
     4: /tmp/babel-hlBzed/C-bin-tb49Ls(+0xceae) [0x563818bc5eae]
     [0] /tmp/babel-hlBzed/C-src-APc5Dz.cpp, line 22, compiled Mar 18 
2021 at 17:20:53
     
--------------------------------------------------------------------------
     MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD
     with errorcode 1.

     NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes.
     You may or may not see output from other processes, depending on
     exactly when Open MPI kills them.
     
--------------------------------------------------------------------------
   #+end_example

   This makes me think that we can have a function (or a template) like 
this:
   #+caption: Fuction to replace =libmesh_error_msg= macro
   #+begin_src cpp :libs $(libmesh-config --cxxflags --include --ldflags 
--libs)
     #include <stdio.h>
     #include <iostream>
     #include "libmesh/libmesh.h"
     #include "libmesh/mesh.h"

     void libmesh_error_msg_fun(std::string &msg) {
       do {
         libMesh::err << msg << std::endl;
         std::stringstream msg_stream;
         msg_stream << msg;
         libMesh::MacroFunctions::report_error(__FILE__, __LINE__, 
LIBMESH_DATE, LIBMESH_TIME);
         LIBMESH_THROW(libMesh::LogicError(msg_stream.str()));
       } while (0);
     }

     template<typename X, typename Y>
     int libmesh_example_requires(X condition, Y option){
       do {
         if (!(condition)) {
           libMesh::out <<
             "Configuring libMesh with " <<
             option <<
             " is required to run this example." << std::endl;
           return 77;
         }
       } while (0);
     }

     int main (int argc, char * argv[]){
       libMesh::LibMeshInit init(argc, argv);

       if (argc < 4){
         std::string msg = {"Usage: "};
         libmesh_error_msg_fun(msg);
       }
     }
   #+end_src

   #+RESULTS:

   #+begin_example
     Usage:
     Stack frames: 6
     0: libMesh::print_trace(std::ostream&)
     1: libMesh::MacroFunctions::report_error(char const*, int, char 
const*, char const*)
     2: /tmp/babel-CpgWD6/C-bin-mEeZoe(+0xcf4f) [0x55567f87ef4f]
     3: /tmp/babel-CpgWD6/C-bin-mEeZoe(+0xcd76) [0x55567f87ed76]
     4: __libc_start_main
     5: /tmp/babel-CpgWD6/C-bin-mEeZoe(+0xcdbe) [0x55567f87edbe]
     [0] /tmp/babel-CpgWD6/C-src-HfTgSq.cpp, line 18, compiled Mar 18 
2021 at 20:48:30
     
--------------------------------------------------------------------------
     MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD
     with errorcode 1.

     NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes.
     You may or may not see output from other processes, depending on
     exactly when Open MPI kills them.
     
--------------------------------------------------------------------------
   #+end_example

   I was expecting =libMesh::= to work as well, because =libmesh_*_msg= 
look very much like functions, and they are inside a =namespace=. I am 
sure that there is a solid reason for which they were kept as macros, 
and that is why this is a humble suggestion. Thank you.