Am Dienstag, 13. August 2013, 00:13:19 schrieb Stephen Kelly:
> Rolf Eike Beer wrote:
> >> 5)
> >>
> >> This is not nice API:
> >>#if defined (CXXFEATURES_NULLPTR_FOUND)
> >>void *nix = nullptr;
> >>#else /* CXXFEATURES_NULLPTR_FOUND */
> >>void *nix = 0;
> >>#endif /* CXXFEATURES_NULLPTR_FOUND */
> >>
> >> Much better would be:
> >>void *nix = CXXFEATURES_NULLPTR;
> >>
> >> where -DCXXFEATURES_NULLPTR=0 or -DCXXFEATURES_NULLPTR=nullptr.
> >>
> >> See what Qt does for other similar API decisions on what should be
> >> defined to something (like nullptr, constexpr, final etc), and what
> >> should be a 'guard' define like above (eg lambdas, variadic templates
> >> etc).
> >>
> >> Note also that by defining the CXXFEATURES_FINAL to something, you get to
> >> use the 'sealed' extension, which does the same thing, and works with
> >> VC2005. See qcompilerdetection.h.
> >
> > The module returns just a list of CMake flags. How this is passed to the
> > user (header, defines, whatever) is currently something the user must
> > decide. I will not do anything fancy in the testcase for now.
>
> Imagine I wanted to set Grantlee_FINAL to empty or final based on whether
> c++11 was active or not. How would I do that?
>
> I might do this:
>
> # This seems like an API smell. With g++ I want to wrap the add_definitions
> # in a condition for enabling c++11 at all. Does this mean that c++11 #
> features are not made available when using MSVC?
> if(CXX11_COMPILER_FLAGS)
> # Can't use add_compile_options as CXX11_COMPILER_FLAGS is a string, not
> # a list.
> # This means that -std=c++11 is also passed when linking.
> set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXX11_COMPILER_FLAGS}")
>
> if (CXXFeatures_class_override_final_FOUND)
> add_definitions(-DGrantlee_FINAL=final)
> set(_final_defined 1)
> endif()
> endif()
>
> if (NOT _final_defined)
> add_definitions(-DGrantlee_FINAL=)
> endif()
>
>
> Do you have any more-real-world examples of what code using your module
> would look like?
>
> My c++ code would then look like:
>
> struct A Grantlee_FINAL
> {
> int data;
> };
>
> However, now downstreams need to define Grantlee_FINAL to something in order
> to compile. We can help of course by putting Grantlee_FINAL in the
> INTERFACE_COMPILE_DEFINITIONS of Grantlee.That is a problem I did not try to solve now. The idea was to get your targets compiled. Even if your target is a library used by the outside and full of C++11 stuff you can keep the interface clean of C++11 specifics. Having the interface in a full-featured C++11 way is step 2 or 3 on the way. I would like to solve the first step first. Eike
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