[Dune-devel] [Dune] dune & cmake

[Martin Rückl]

Hey,
Since i kind of came up with this whole discussion, i just want to share 
my thoughts again.
First, i think, this http://stackoverflow.com/questions/28637542/ 
<http://stackoverflow.com/questions/28637542/ensure-config-h-is-included-once/28637797#28637797> 
is a pretty good post about the issue. Second, I will just copy paste 
what i think should be kept in mind:

 1. Ususally config.h is only required for building the library and will
    not be exposed to the user (i.e. will not be installed). That
    requires that the library interface does not depend on the config.h
    file. This implies, that usage of #defines from the config.h files
    may only occur within the libraries compiled .cpp files.
 2. Heavy use of template tends to result in code moved from .cpp to
    .hpp files. Hennce, in DUNE, lots of the interface itself depends on
    the variables set during configuration stage.

As pointed out in the SO post, there seems to be no proper solution for 
#2. As mentioned, Eigen3 solves it by putting e.g. its own version 
information into a header file which ships with the installation and is 
included by other header files from the library.
 From the library user point, Ansgars proposal seems to be the correct 
way. There, each module can have its own defines of type #2  
(DUNE_B_HAVE_MPI) and those can ship in a header file which can be 
included by other headers from the library without "messing up the 
global define namespace".

HtH Martin


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