Try to compile the following code.
#include <string>#include <boost/any.hpp>class V{public: V& operator=(int i) { v = i; return *this; } V& operator=(const std::string& s) { v = s; return *this; } operator int() const { return boost::any_cast<int>(v); } operator std::string() const { return boost::any_cast<std::string>(v); }private: boost::any v;};int main(){ V v; std::string s1 = "hello", s2; v = s1; s2 = v;}Below is the error.
$ g++ test__boost_any.cpptest__boost_any.cpp: In function ‘int main()’:test__boost_any.cpp:37:9: error: ambiguous overload for ‘operator=’ (operand types are ‘std::__cxx11::string’ {aka ‘std::__cxx11::basic_string<char>’} and ‘V’) s2 = v; ^In file included from /usr/include/c++/8/string:52, from test__boost_any.cpp:1:/usr/include/c++/8/bits/basic_string.h:668:7: note: candidate: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ operator=(const basic_string& __str) ^~~~~~~~/usr/include/c++/8/bits/basic_string.h:718:7: note: candidate: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(_CharT) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ operator=(_CharT __c) ^~~~~~~~/usr/include/c++/8/bits/basic_string.h:736:7: note: candidate: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ operator=(basic_string&& __str) ^~~~~~~~