foo.cc: In function ‘int main()’:
foo.cc:6:11: error: no match for ‘operator<<’ (operand types are ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} and ‘int’)
    6 |     cin>>a<<b;
      |     ~~~~~~^~~
      |        |    |
      |        |    int
      |        std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}
foo.cc:6:11: note: there are 61 candidates
    6 |     cin>>a<<b;
      |     ~~~~~~^~~
foo.cc:6:11: note: candidate 1: ‘operator<<(int, int)’ (built-in)
foo.cc:6:11: note: no known conversion for argument 1 from ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} to ‘int’
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/regex:70,
                 from stdc++.h:184:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/regex.h:1737:5: note: candidate 2: ‘template<class _Ch_type, class _Ch_traits, class _Bi_iter> std::basic_ostream<_CharT, _Traits>& std::__cxx11::operator<<(std::basic_ostream<_CharT, _Traits>&, const sub_match<_Bi_iter>&)’
 1737 |     operator<<(basic_ostream<_Ch_type, _Ch_traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/regex.h:1737:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/string:56,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/bitset:54,
                 from stdc++.h:54:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/basic_string.h:4367:5: note: candidate 3: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
 4367 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/basic_string.h:4367:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bitset:1692:5: note: candidate 4: ‘template<class _CharT, class _Traits, long unsigned int _Nb> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const bitset<_Nb>&)’
 1692 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bitset:1692:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/bits/ios_base.h:48,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/streambuf:45,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/bits/streambuf_iterator.h:37,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/iterator:68,
                 from stdc++.h:56:
/nix/gcc-15.2.0/include/c++/15.2.0/system_error:341:5: note: candidate 5: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)’
  341 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/system_error:341:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/memory:82,
                 from stdc++.h:58:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/shared_ptr.h:70:5: note: candidate 6: ‘template<class _Ch, class _Tr, class _Tp, __gnu_cxx::_Lock_policy _Lp> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __shared_ptr<_Tp, _Lp>&)’
   70 |     operator<<(std::basic_ostream<_Ch, _Tr>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/shared_ptr.h:70:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/ostream:42,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/istream:43,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/sstream:42,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/complex:50,
                 from /nix/gcc-15.2.0/include/c++/15.2.0/ccomplex:43,
                 from stdc++.h:133:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:626:5: note: candidate 7: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)’
  626 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:626:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:636:5: note: candidate 8: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)’
  636 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:636:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:642:5: note: candidate 9: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)’
  642 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:642:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:653:5: note: candidate 10: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)’
  653 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:653:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:658:5: note: candidate 11: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)’
  658 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:658:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:717:5: note: candidate 12: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)’
  717 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:717:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/ostream:294:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.tcc:311:5: note: candidate 13: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)’
  311 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.tcc:311:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:734:5: note: candidate 14: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)’
  734 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:734:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:747:5: note: candidate 15: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)’
  747 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:747:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:752:5: note: candidate 16: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)’
  752 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:752:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:836:5: note: candidate 17: ‘template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)’
  836 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:836:5: note: template argument deduction/substitution failed:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h: In substitution of ‘template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_istream<char>&; _Tp = int]’:
foo.cc:6:13:   required from here
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/ostream.h:836:5: error: no type named ‘type’ in ‘struct std::enable_if<false, void>’
  836 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/complex:597:5: note: candidate 18: ‘template<class _Tp, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const complex<_Tp>&)’
  597 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const complex<_Tp>& __x)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/complex:597:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from stdc++.h:146:
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:89:5: note: candidate 19: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Resetiosflags)’
   89 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Resetiosflags __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:89:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:119:5: note: candidate 20: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setiosflags)’
  119 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:119:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:153:5: note: candidate 21: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setbase)’
  153 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setbase __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:153:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:190:5: note: candidate 22: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setfill<_CharT>)’
  190 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setfill<_CharT> __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:190:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:220:5: note: candidate 23: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setprecision)’
  220 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:220:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:250:5: note: candidate 24: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setw)’
  250 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setw __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:250:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:323:5: note: candidate 25: ‘template<class _CharT, class _Traits, class _MoneyT> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Put_money<_MoneyT>)’
  323 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_money<_MoneyT> __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:323:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:375:5: note: candidate 26: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Put_time<_CharT>)’
  375 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_time<_CharT> __f)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/iomanip:375:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/valarray:607,
                 from stdc++.h:169:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: candidate 27: ‘template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: candidate 28: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: candidate 29: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘int’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: candidate 30: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: candidate 31: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/valarray_after.h:415:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘int’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: candidate 32: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const valarray<_Tp>&, const valarray<_Tp>&)’
 1206 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::valarray<_Tp>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: candidate 33: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)’
 1206 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::valarray<_Tp>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: candidate 34: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)’
 1206 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/valarray:1206:1: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   mismatched types ‘const std::valarray<_Tp>’ and ‘int’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/random:50,
                 from stdc++.h:182:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.h:1443:5: note: candidate 35: ‘template<class _RandomNumberEngine, long unsigned int __w, class _UIntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const independent_bits_engine<_RandomNumberEngine, __w, _UIntType>&)’
 1443 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.h:1443:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from /nix/gcc-15.2.0/include/c++/15.2.0/random:52:
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:910:5: note: candidate 36: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const uniform_int_distribution<_IntType>&)’
  910 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:910:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:968:5: note: candidate 37: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const uniform_real_distribution<_IntType>&)’
  968 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:968:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2145:5: note: candidate 38: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const cauchy_distribution<_RealType>&)’
 2145 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2145:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1029:5: note: candidate 39: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const bernoulli_distribution&)’
 1029 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1029:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1110:5: note: candidate 40: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const geometric_distribution<_IntType>&)’
 1110 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1110:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1762:5: note: candidate 41: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const exponential_distribution<_RealType>&)’
 1762 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1762:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2539:5: note: candidate 42: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const weibull_distribution<_RealType>&)’
 2539 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2539:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2613:5: note: candidate 43: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const extreme_value_distribution<_RealType>&)’
 2613 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2613:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:156:5: note: candidate 44: ‘template<class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const linear_congruential_engine<_UIntType, __a, __c, __m>&)’
  156 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:156:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:477:5: note: candidate 45: ‘template<class _UIntType1, long unsigned int __w1, long unsigned int __n1, long unsigned int __m1, long unsigned int __r1, _UIntType1 __a1, long unsigned int __u1, _UIntType1 __d1, long unsigned int __s1, _UIntType1 __b1, long unsigned int __t1, _UIntType1 __c1, long unsigned int __l1, _UIntType1 __f1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>&)’
  477 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:477:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:635:5: note: candidate 46: ‘template<class _UIntType, long unsigned int __w, long unsigned int __s, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const subtract_with_carry_engine<_UIntType, __w, __s, __r>&)’
  635 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:635:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:704:5: note: candidate 47: ‘template<class _RandomNumberEngine, long unsigned int __p, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const discard_block_engine<_RandomNumberEngine, __p, __r>&)’
  704 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:704:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:866:5: note: candidate 48: ‘template<class _RandomNumberEngine, long unsigned int __k, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const shuffle_order_engine<_RandomNumberEngine, __k>&)’
  866 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:866:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1224:5: note: candidate 49: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const negative_binomial_distribution<_IntType>&)’
 1224 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1224:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1434:5: note: candidate 50: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const poisson_distribution<_IntType>&)’
 1434 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1434:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1700:5: note: candidate 51: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const binomial_distribution<_IntType>&)’
 1700 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1700:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1920:5: note: candidate 52: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const normal_distribution<_RealType>&)’
 1920 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1920:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1987:5: note: candidate 53: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const lognormal_distribution<_RealType>&)’
 1987 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:1987:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2059:5: note: candidate 54: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const chi_squared_distribution<_RealType>&)’
 2059 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2059:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2220:5: note: candidate 55: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const fisher_f_distribution<_RealType>&)’
 2220 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2220:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2294:5: note: candidate 56: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const student_t_distribution<_RealType>&)’
 2294 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2294:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2463:5: note: candidate 57: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const gamma_distribution<_RealType>&)’
 2463 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2463:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2749:5: note: candidate 58: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const discrete_distribution<_IntType>&)’
 2749 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2749:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2971:5: note: candidate 59: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const piecewise_constant_distribution<_RealType>&)’
 2971 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:2971:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:3177:5: note: candidate 60: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const piecewise_linear_distribution<_RealType>&)’
 3177 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/bits/random.tcc:3177:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
In file included from stdc++.h:187:
/nix/gcc-15.2.0/include/c++/15.2.0/thread:107:5: note: candidate 61: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, thread::id)’
  107 |     operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
      |     ^~~~~~~~
/nix/gcc-15.2.0/include/c++/15.2.0/thread:107:5: note: template argument deduction/substitution failed:
foo.cc:6:13: note:   ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |     cin>>a<<b;
      |             ^
foo.cc:9:5: warning: this ‘else’ clause does not guard... [-Wmisleading-indentation]
    9 |     else
      |     ^~~~
foo.cc:11:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘else’
   11 |         return 0;
      |         ^~~~~~