On 1/3/06, Alexander Nasonov <alnsn@yandex.ru> wrote:
There are two problems with void returns.
1. A couple of examples in documentation are inaccurate: main returns void. The fix is
$ cd $BOOST_ROOT/libs/typeof/doc $ sed 's/void main/int main/' typeof.qbk
2. BOOST_TYPEOF can't be applied to an expression returning void.
void foo() {} int main() { BOOST_TYPEOF(foo()); // Error: ensure_obj doesn't accept void as an argument. }
The patch below fixes this problem. It's built around comma operator:
struct void_ {}; template<class T> T& operator,(T const&, void_);
How will this work if someone implements their own operator,? template<class T> T& operator,(const my_type&,const T&); if expr equals my_type, wouldn't this break typeof for my_type? Peder
template<class T> T& ensure_obj(const T&); void ensure_obj(void_);
Return type of an expression ((expr), void_()) is T&, if typeof(expr) == T && T != void void_, if typeof(expr) == void
I ran tests on gcc 3.4.4 under FreeBSD. All tests passed. I haven't tried to analyze the problem on MSVC.
Let me know if fixes are fine and I'll commit them.
$ cvs diff -u boost/typeof/typeof.hpp alnsn@cvs.sourceforge.net's password: Index: boost/typeof/typeof.hpp =================================================================== RCS file: /cvsroot/boost/boost/boost/typeof/typeof.hpp,v retrieving revision 1.3 diff -u -r1.3 typeof.hpp --- boost/typeof/typeof.hpp 28 Sep 2005 03:47:05 -0000 1.3 +++ boost/typeof/typeof.hpp 3 Jan 2006 21:51:47 -0000 @@ -128,10 +128,15 @@ # ifndef MSVC_TYPEOF_HACK
namespace boost { namespace type_of { + struct void_ {}; + template<class T> T& operator,(T const&, void_); template<class T> T& ensure_obj(const T&); + void ensure_obj(void_); }}
-# define BOOST_TYPEOF(expr) BOOST_TYPEOF_KEYWORD(boost::type_of::ensure_obj(expr)) +# define BOOST_TYPEOF(expr) BOOST_TYPEOF_KEYWORD( \ + boost::type_of::ensure_obj( ((expr), boost::type_of::void_()) ) \ + ) # define BOOST_TYPEOF_TPL BOOST_TYPEOF # endif # define BOOST_TYPEOF_REGISTER_TYPE(x)
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