문제는 당신 value_type
가 실제로std::pair
(그리고 하나에 암시 적으로 변환되지 않습니다), 따라서 전달 될 수 없다는 것입니다 :
typedef boost::bimap<unsigned int, boost::shared_ptr<A> > container_type;
typedef container_type::left_const_iterator base_const_iterator;
typedef boost::transform_iterator<makeIterConst<A>, base_const_iterator> const_iterator;
template <typename T>
struct makeIterConst : std::unary_function<std::pair<unsigned int const, boost::shared_ptr<T> const>, std::pair<unsigned int const, boost::shared_ptr<T const> const> >
{
std::pair<unsigned int const, boost::shared_ptr<T const> const> operator() (std::pair<int const, boost::shared_ptr<T> const> const & orig) const
{
std::pair<int const, boost::shared_ptr<T const> const> newPair(orig.first, boost::const_pointer_cast<T const>(orig.second));
return newPair;
}
};
다음은 "핵심"오류입니다 makeIterConst::operator()
.
대신 const base_const_iterator::value_type &
으로 만듭니다.
#include <iostream>
#include <string>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <boost/bimap.hpp>
#include <boost/iterator/transform_iterator.hpp>
struct A
{
std::string data;
A(const std::string& s) : data(s) {}
};
typedef boost::bimap<unsigned int, boost::shared_ptr<A> > container_type;
typedef container_type::left_map::const_iterator base_const_iterator;
template <typename T>
struct makeIterConst : std::unary_function<base_const_iterator::value_type const &,
std::pair<unsigned int const, boost::shared_ptr<T const> const> >
{
std::pair<unsigned int const, boost::shared_ptr<T const> const> operator()
(base_const_iterator::value_type const & orig) const
{
std::pair<int const, boost::shared_ptr<T const> const> newPair(orig.first, boost::const_pointer_cast<T const>(orig.second));
return newPair;
}
};
typedef boost::transform_iterator<makeIterConst<A>,
base_const_iterator> const_iterator;
int main()
{
container_type m;
boost::shared_ptr<A> p = boost::make_shared<A>("foo");
m.insert(container_type::value_type(1, p));
// using regular iterator
for(base_const_iterator left_iter = m.left.begin();
left_iter != m.left.end();
++left_iter)
{
std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
left_iter->second->data = "bar"; // compiles
}
// using constified iterator
for(const_iterator left_iter = boost::make_transform_iterator(m.left.begin(), makeIterConst<A>());
left_iter != boost::make_transform_iterator(m.left.end(), makeIterConst<A>());
++left_iter)
{
std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
// the following will give a compilation error, as expected
// left_iter->second->data = "changed_foo";
}
}
시험 : https://ideone.com/fHIUe