[Boost-users] BUG/PATCH: Spurious warning in boost::xpressive::detail::enable_reference_tracking

From: Bryan Donlan (bdonlan_at_[hidden])
Date: 2007-09-03 20:20:28

Creating a static xpressive regex object referencing statically
another regex object causes a spurious (and often extremely long)
warning when gcc's -W and -Wall flags are in use.

GCC version: version 4.1.3 20070831 (prerelease) (Ubuntu 4.1.2-16ubuntu1)
boost version: 1.34.0 and 1.34.1

To demonstrate this bug, build the following on -W -Wall:
--- boostbug.cc ---
#include <boost/xpressive/xpressive.hpp>

int main() {
    boost::xpressive::sregex r1 = boost::xpressive::digit;
    boost::xpressive::sregex r2 = *r1;
    return 0;
}

--- end boostbug.cc ---

The warning output is as follows:
/usr/include/boost/xpressive/detail/utility/tracking_ptr.hpp: In copy
constructor 'boost::xpressive::detail::enable_reference_tracking<Derived>::enable_reference_tracking(const
boost::xpressive::detail::enable_reference_tracking<Derived>&) [with
Derived = boost::xpressive::detail::regex_impl<__gnu_cxx::__normal_iterator<const
char*, std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > >]':
/usr/include/boost/xpressive/detail/core/regex_impl.hpp:63:
instantiated from
'boost::xpressive::detail::regex_impl<BidiIter>::regex_impl(const
boost::xpressive::detail::regex_impl<BidiIter>&) [with BidiIter =
__gnu_cxx::__normal_iterator<const char*, std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >]'
/usr/include/boost/xpressive/detail/utility/tracking_ptr.hpp:173:
instantiated from 'void
boost::xpressive::detail::enable_reference_tracking<Derived>::tracking_clear()
[with Derived =
boost::xpressive::detail::regex_impl<__gnu_cxx::__normal_iterator<const
char*, std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > >]'
/usr/include/boost/xpressive/detail/utility/tracking_ptr.hpp:395:
instantiated from 'boost::xpressive::detail::tracking_ptr<Type>&
boost::xpressive::detail::tracking_ptr<Type>::operator=(const
boost::xpressive::detail::tracking_ptr<Type>&) [with Type =
boost::xpressive::detail::regex_impl<__gnu_cxx::__normal_iterator<const
char*, std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > >]'
/usr/include/boost/xpressive/detail/utility/tracking_ptr.hpp:373:
instantiated from
'boost::xpressive::detail::tracking_ptr<Type>::tracking_ptr(const
boost::xpressive::detail::tracking_ptr<Type>&) [with Type =
boost::xpressive::detail::regex_impl<__gnu_cxx::__normal_iterator<const
char*, std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > >]'
/usr/include/boost/xpressive/basic_regex.hpp:53:   instantiated from
'boost::xpressive::basic_regex<BidiIter>::basic_regex(const
boost::xpressive::basic_regex<BidiIter>&) [with BidiIter =
__gnu_cxx::__normal_iterator<const char*, std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >]'
boostbug.cc:4:   instantiated from here
/usr/include/boost/xpressive/detail/utility/tracking_ptr.hpp:205:
warning: base class 'class
boost::enable_shared_from_this<boost::xpressive::detail::regex_impl<__gnu_cxx::__normal_iterator<const
char*, std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > > >' should be explicitly initialized in the
copy constructor

I've attached a trivial patch (against 1.34.0; applies cleanly to
1.34.1) to silence this warning.