boost::gregorian::date_iterator missing postfix operators ++ and --

[dkochin@…]

/* Consider the following (somewhat canonical) code snippet */ {

std::vector<boost::gregorian::date> dates(count); auto dt_i = dates.begin(); boost::gregorian::month_iterator m_i(some_start_date, 1);

while (dt_i != dts.end())

*dt_i++ = *m_i++; /* this will call prefix ++ operator on m_i

leading to subtle bug */

}

[James E. King, III]

Test (unsure if return is correct; will move into unit test before submitting PR):

#include <boost/date_time/gregorian/gregorian.hpp>

int main()
{
    boost::gregorian::date some_date(2007, 8, 9);
    boost::gregorian::month_iterator m_i(some_date, 1);
    boost::gregorian::greg_month m(1);
    m = *m_i++;
    return !(m == 8);
}

When building with gcc-7.2 and -Wall:

gcc.compile.c++ ../../../bin.v2/libs/date_time/test/testdate_iterator.test/gcc-gnu-7/debug/threadapi-pthread/gregorian/testdate_iterator.o
gregorian/testdate_iterator.cpp: In function ‘int main()’:
gregorian/testdate_iterator.cpp:63:20: error: no ‘operator++(int)’ declared for postfix ‘++’ [-fpermissive]
     date chk = *m_i++;
                 ~~~^~
gregorian/testdate_iterator.cpp:67:15: error: no ‘operator--(int)’ declared for postfix ‘--’ [-fpermissive]
     chk = *m_i--;
            ~~~^~

    "g++"   -O0 -fno-inline -Wall -g -fPIC -m64 -Wunused-local-typedefs -DBOOST_ALL_NO_LIB -DBOOST_ALL_NO_LIB=1 -DBOOST_DATE_TIME_POSIX_TIME_STD_CONFIG -DBOOST_DATE_TIME_STATIC_LINK -DDATE_TIME_INLINE  -I"../../.." -c -o "../../../bin.v2/libs/date_time/test/testdate_iterator.test/gcc-gnu-7/debug/threadapi-pthread/gregorian/testdate_iterator.o" "gregorian/testdate_iterator.cpp"

[James E. King, III]

postfix operator implementation requires return-by-value, and in this case the get_offset and get_neg_offset methods are pure virtual, making that impossible in the current implementation.