answer.code: In member function ‘void RegExp::init() const’:
answer.code:573:41: error: no match for ‘operator=’ (operand types are ‘const regex’ {aka ‘const std::__cxx11::basic_regex<char>’} and ‘std::__cxx11::regex’ {aka ‘std::__cxx11::basic_regex<char>’})
  573 |     this->regex=std::regex(plain.c_str());
      |                                         ^
In file included from /usr/include/c++/11/regex:63,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:110,
                 from answer.code:1:
/usr/include/c++/11/bits/regex.h:574:9: note: candidate: ‘template<class _Ch_traits, class _Alloc> std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >& std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >::operator=(const std::__cxx11::basic_string<_Ch_type, _Ch_traits, _Ch_alloc>&) [with _Ch_traits = _Ch_traits; _Alloc = _Alloc; _Ch_type = char; _Rx_traits = std::__cxx11::regex_traits<char>]’
  574 |         operator=(const basic_string<_Ch_type, _Ch_traits, _Alloc>& __s)
      |         ^~~~~~~~
/usr/include/c++/11/bits/regex.h:574:9: note:   template argument deduction/substitution failed:
answer.code:573:41: note:   ‘std::__cxx11::regex’ {aka ‘std::__cxx11::basic_regex<char>’} is not derived from ‘const std::__cxx11::basic_string<char, _Ch_traits, _Ch_alloc>’
  573 |     this->regex=std::regex(plain.c_str());
      |                                         ^
In file included from /usr/include/c++/11/regex:63,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:110,
                 from answer.code:1:
/usr/include/c++/11/bits/regex.h:533:7: note: candidate: ‘std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >& std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >::operator=(const std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >&) [with _Ch_type = char; _Rx_traits = std::__cxx11::regex_traits<char>]’ (near match)
  533 |       operator=(const basic_regex& __rhs)
      |       ^~~~~~~~
/usr/include/c++/11/bits/regex.h:533:7: note:   passing ‘const regex*’ {aka ‘const std::__cxx11::basic_regex<char>*’} as ‘this’ argument discards qualifiers
/usr/include/c++/11/bits/regex.h:540:7: note: candidate: ‘std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >& std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >::operator=(std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >&&) [with _Ch_type = char; _Rx_traits = std::__cxx11::regex_traits<char>]’ (near match)
  540 |       operator=(basic_regex&& __rhs) noexcept
      |       ^~~~~~~~
/usr/include/c++/11/bits/regex.h:540:7: note:   passing ‘const regex*’ {aka ‘const std::__cxx11::basic_regex<char>*’} as ‘this’ argument discards qualifiers
/usr/include/c++/11/bits/regex.h:551:7: note: candidate: ‘std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >& std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >::operator=(const _Ch_type*) [with _Ch_type = char; _Rx_traits = std::__cxx11::regex_traits<char>]’
  551 |       operator=(const _Ch_type* __p)
      |       ^~~~~~~~
/usr/include/c++/11/bits/regex.h:551:33: note:   no known conversion for argument 1 from ‘std::__cxx11::regex’ {aka ‘std::__cxx11::basic_regex<char>’} to ‘const char*’
  551 |       operator=(const _Ch_type* __p)
      |                 ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/11/bits/regex.h:563:7: note: candidate: ‘std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >& std::__cxx11::basic_regex< <template-parameter-1-1>, <template-parameter-1-2> >::operator=(std::initializer_list<_Tp>) [with _Ch_type = char; _Rx_traits = std::__cxx11::regex_traits<char>]’
  563 |       operator=(initializer_list<_Ch_type> __l)
      |       ^~~~~~~~
/usr/include/c++/11/bits/regex.h:563:44: note:   no known conversion for argument 1 from ‘std::__cxx11::regex’ {aka ‘std::__cxx11::basic_regex<char>’} to ‘std::initializer_list<char>’
  563 |       operator=(initializer_list<_Ch_type> __l)
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~