C ++与boost :: ptr_map / boost :: checked_delete交友失败

#include <boost/checked_delete.hpp>
#include <boost/ptr_container/ptr_map.hpp>


class foo
{
    friend void boost::checked_delete<>(foo*);
    ~foo() {}
};


int main()
{
    boost::checked_delete(new foo);     // OK
    boost::ptr_map<int, foo> foo_map;   // error C2248: \'foo::~foo\' : cannot access private member declared in class \'foo\'

    return 0;
}

// verify that types are complete for increased safety

template<class T> inline void checked_delete(T * x)
{
    // intentionally complex - simplification causes regressions
    typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
    (void) sizeof(type_must_be_complete);
    delete x;    // error C2248
}