------- Additional Comments From jmegq at radiance dot com 2005-09-02 00:16
-------
Regarding macros -- I just found out about the _Pragma directive from C99, so at
least you can do something like this (paraphrasing some ACE code):
#define EXPORT_SINGLETON_DECLARE (SINGLETON_TYPE, CLASS, LOCK) \
_Pragma ("GCC visibility push(default)") \
template class SINGLETON_TYPE <CLASS, LOCK>; \
_Pragma ("GCC visibility pop")
#define IMPORT_SINGLETON_DECLARE(SINGLETON_TYPE, CLASS, LOCK) extern template
class SINGLETON_TYPE <CLASS, LOCK>;
Then define SINGLETON_DECLARE to depending on whether you're building the lib or
not.
A possible issue with this is that it must come before, say, a typedef of the
template type. The example below works on VS but not g++ (not that VS matters,
but I'm using code that does this):
typedef Singleton_T<Foo, Mutex> FOO_SINGLETON;
SINGLETON_DECLARE(Singleton_T, Foo, Mutex)
Instead, the SINGLETON_DECLARE needs to come before the typedef or it will get
hidden visibility on g++. I'm curious as to why the typedef causes the symbols
to get hidden visibility -- is that in spec, or is a bug?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470
