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c++boostmacrosnamespacesboost-hana

Why does Boost.Hana use macros for opening/closing namespaces?

One of the many examples of two macros being used to open and close a namespace respectively is in /usr/include/boost/hana/transform.hpp:

BOOST_HANA_NAMESPACE_BEGIN
// stuff
BOOST_HANA_NAMESPACE_END

Those macros are defined like this in /usr/include/boost/hana/config.hpp:

#define BOOST_HANA_NAMESPACE_BEGIN namespace boost { namespace hana {

#define BOOST_HANA_NAMESPACE_END }}

What is the advantage of doing so?

(Considering that there's at least one disvantage: that it makes it harder to jump back and forth from beginning to end of namespaces.)

Solution

  • This was originally for forward compatibility with using inline namespaces, however this never became relevant. I re-opened https://github.com/boostorg/hana/issues/288 and will change it to normal namespace declarations.