id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
5273,question about fusion and documentation,ramey@…,danmarsden,"I'm having a problem distinguishing the difference between metafunctions at_key and value_at_key. The documentation for value_at_key shows the following example:

{{{
typedef map<pair<int, char>, pair<char, char>, pair<double, char> > mymap;
BOOST_MPL_ASSERT((boost::is_same<result_of::at_key<mymap, int>::type, char>));
}}}

note the absence of value_at_key in the example!
while the example in at_key shows

{{{
typedef map<pair<int, char>, pair<char, char>, pair<double, char> > mymap;
BOOST_MPL_ASSERT((boost::is_same<result_of::at_key<mymap, int>::type, char&>));
}}}

I see the & indicating a reference, but I can't see how this would be any different than using add_reference to the result of at_value_key.

Any little bit of light you might want shed here would be helpful.  At the very least, I think the documention should be clarified.

Robert Ramey

",Bugs,closed,To Be Determined,fusion,Boost 1.45.0,Problem,fixed,,