Advanced C++ Programming Cookbook

How it works...

Move-only classes prevent a class from being copied, which in some cases, can be a performance improvement. Move-only classes also ensure a 1:1 relationship between resources that are created versus the resources that are allocated, as copies cannot exist. Moving a class, however, can result in a class becoming invalid, as in this example:

#include <iostream>class the_answer{    std::unique_ptr<int> m_answer;public:    explicit the_answer(int answer) :        m_answer{std::make_unique<int>(answer)}    { }    ~the_answer()    {        std::cout << "The answer is: " << *m_answer << '\n';    }public:    the_answer(the_answer &&other) noexcept = default;    the_answer &operator=(the_answer &&other) noexcept = default;};int main(void){    the_answer is_42{42}; the_answer ...