#include <iostream>
#include <cstdlib>
#include <string>#include <variant>
#include <array>
#include <cstring> //for std::strlen
#include <string_view>class String{
private:enum{ object_size = sizeof(std::string) };using string=std::string;using array=std::array<char,object_size> ;std::variant<std::monostate, string, array > data_;void set_data(const char* src){if (src==nullptr){data_.emplace<array>();auto& a = std::get<array>(data_);a[0]=0;}else if (std::strlen(src)>=object_size){data_.emplace<string>(src);}else{data_.emplace<array>();auto& a = std::get<array>(data_);std::copy(src,src+std::strlen(src),a.begin());a[std::strlen(src)]=0;}}public:String(const char* src){set_data(src);}void operator=(const char* src){set_data(src);}const char* c_str(){const char* ret = nullptr;switch (data_.index()){case 1:ret = std::get<string>(data_).c_str();break;case 2:ret = std::get<array>(data_).begin();break;}return ret;}std::string_view str(){switch (data_.index()){case 0:return std::string_view();case 1:return std::string_view(std::get<string>(data_));case 2:return std::string_view(std::get<array>(data_).begin());}}
};int main()
{  String s("12345");std::cout << s.c_str() << std::endl;s = "..............................hello world!";auto v1 = s.str();auto v2 = v1.substr(v1.find_first_not_of('.'));std::cout << v2 << std::endl;
}

char buf_[64];
new (buf_) std::string("12345");
reinterpret_cast<std::string*>(buf_)->~basic_string();