Well, my mpl adventure continues.
I'm trying to place pair members of a sequence with their keys:
#include
#include
#include
#include
#include
#include
#include
#include <iostream>
#include <typeinfo>
using namespace boost;
using namespace boost::mpl;
struct pair_base {};
template
struct pair_type : public pair, private pair_base {};
template<typename Sequence>
struct replaceit {
typedef typename replace_if<
Sequence,
is_base_and_derived,
key_type, _>
>::type type;
};
int main(void)
{
replaceit<
vector<
charm
pair_type >,
pair_type >
double
>
>::type toprint;
std::cout << typeid(toprint).name() << std::endl;
return(0);
};
I know this is incorrect because the pairs will be replaced by
the key_type metafunction itself.
If I add ::type to the end of key_type, _> the compiler
complains that no ::first member exists:
boost-1_32/boost/mpl/pair.hpp: In instantiation of
`boost::mpl::first':
replace.cc:25: instantiated from
`boost::mpl::key_type_implboost::mpl::aux::map_tag::apply, mpl_::_>'
replace.cc:25: instantiated from
`boost::mpl::key_type, mpl_::_>'
replace.cc:25: instantiated from here
boost-1_32/boost/mpl/pair.hpp:43: no
type named `first' in `struct mpl_::_'
What's the right way to do this?
Furthermore, is there a better way to identify pairs in
replace_if than deriving from a special class? All I can
think of is writing a predicate class and specializing it
for mpl::pair. Seems like there should be an easier
way.
Thanks!
-Dave
