Jean-Louis Leroy wrote:
How can I create a map that has the same content as another rmap, except
for a given key which has a new associated value ? I'm looking for
something like replace_key<Key>(Sequence, Value) in the doc but I cannot
find it. I think I can build it with push_back(erase_key<Key>(seq),
make_pair<Key>(newval)) but if it already exists...
I'm encountering difficulties while trying to implement this. Consider :
template<class K>
struct replace_at_key {
template<typename Any> bool operator()(Any) const { return false; }
template<class V> bool operator()(boost::fusion::pair) const
{ return true; }
};
void test() {
using namespace boost::fusion;
typedef map<
pair
, pair >
map_type;
map_type m(
make_pair<int>("X")
, make_pair<double>("Men"));
BOOST_AUTO(v, boost::fusion::as_vector(
replace_if(m, replace_at_key<int>(),
make_pair("Z"))));
as_map(v); // error : reference to reference
}
I get compiler errors (msvc9 and g++ 4.4.1) because it's trying to form
a reference to a reference. Indeed, when I look inside v with the
debugger I see that the type of v.vec.m1 is
`const pair&' (note : reference). And m1 is passed by
reference in the internals of fusion. Hence the error.
Am I doing something wrong here ?
Thanks,
J-L
