Modified cmake projects

[phlptp]

update the cmake to only allow 1 of the static/shared/object/ header only to be built

Make some tests run against the shared library and fix that up so it actually works properly.

[codecov-commenter]

Codecov Report

Merging #155 (a03421a) into master (db614a5) will not change coverage.
The diff coverage is n/a.

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##           master     #155   +/-   ##
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  Coverage   99.25%   99.25%           
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  Files           6        6           
  Lines        4809     4809           
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  Hits         4773     4773           
  Misses         36       36           

[phlptp]

finish up fixes and recommendations from #153 and add tests for the shared library and install packages

[phlptp]

@kerim371 can you take a look through these changes and see if they match up with your recommendations

[kerim371]

@phlptp hi,

Thank you for these improvements. I have tested it.
I liked the changes you made like (correct me if I'm wrong):

1. now all the units target is placed in a namespace units::units and this name stays the same no matter wether we build static or shared library;
2. after installation units headers are placed in the directory: install/units/*.hpp and thus we include headers as #include <units/units.hpp>;
3. generated units_export.h is placed in install/units/units_export.h and thus we don't get any errors telling that compiler can't find units_export.h. The only thing is that units_decl.hpp includes units_export.h as:

#include "units/units_export.h"

but both files units_decl.hpp and units_export.h are located in the same folder. I have checked it works fine in any case (#include "units/units_export.h" or #include "units_export.h") but I guess (I don't know exactly) it should be included as #include "units_export.h" as they are located in the same directory.

Also I have left some meaningful comments on changed files. Please look at them

[kerim371]

The block:

if(NOT UNITS_HEADER_ONLY)
...
endif(NOT UNITS_HEADER_ONLY)

looks a little hardcoded but I can't propose anything better.

The only thing I can propose is to check whether the developper have checked ON only one option from these three (UNITS_BUILD_STATIC_LIBRARY , UNITS_BUILD_SHARED_LIBRARY, UNITS_HEADER_ONLY) and if there are for example both UNITS_BUILD_STATIC_LIBRARY =ON and UNITS_BUILD_SHARED_LIBRARY=ON we could send a message (WARNING or even FATAL_ERROR) telling that only one library at a time can be built.
Without this it is difficult to predict how the library is going to be built (shared/static/header_only or their combinations) and the developper would need to skim the cmake code to figure that out.

[phlptp]

I added some warnings to check if more than one of UNITS_BUILD_STATIC_LIBRARY, UNITS_BUILD_SHARED_LIBRARY, and UNITS_BUILD_OBJECT_LIBRARY is set, and if you set all three you will get two warnings.

[phlptp]

@kerim371 I am going to merge this and do a few more things to get an updated release out soon. If you have any more suggestions or tweaks let me know.

Thanks