Why can't I do assignment with program_options::options_description?

[Matthew Busche]

Hi,

Why won't this compile?

#include "boost/program_options.hpp"

int main(int argc, char** argv)
{
    boost::program_options::options_description od1;
    boost::program_options::options_description od2;
    od2 = od1;
    return 0;
}

g++ 4.8.4 on ubuntu gives this error:

>  g++ foo.cpp -std=c++11 -lboost_program_options
foo.cpp: In function ‘int main(int, char**)’:
foo.cpp:7:9: error: use of deleted function ‘boost::program_options::options_description& boost::program_options::options_description::operator=(const boost::program_options::options_description&)’
     od2 = od1;
         ^
In file included from /usr/include/boost/program_options.hpp:15:0,
                 from foo.cpp:1:
/usr/include/boost/program_options/options_description.hpp:173:38: note: ‘boost::program_options::options_description& boost::program_options::options_description::operator=(const boost::program_options::options_description&)’ is implicitly deleted because the default definition would be ill-formed:
     class BOOST_PROGRAM_OPTIONS_DECL options_description {
                                      ^
/usr/include/boost/program_options/options_description.hpp:173:38: error: non-static const member ‘const unsigned int boost::program_options::options_description::m_line_length’, can’t use default assignment operator
/usr/include/boost/program_options/options_description.hpp:173:38: error: non-static const member ‘const unsigned int boost::program_options::options_description::m_min_description_length’, can’t use default assignment operator

Curiously, the copy constructor does compile. I'm getting ready to redesign some things to avoid the copy-assign, but I don't understand why this should be disallowed.

Thanks,
Matt Busche

[Matthew Busche]

Never mind -- the last bit of compiler output was actually useful -- options_description has const data members that's breaking operator=(). That's annoying. I'm going to have to design around this.