singleton.cpp

#include <iostream>
#include <string>

class Singleton {
public:
    // Returns a reference to static instance of this class
    static Singleton& instance() {
        static Singleton instance;
        return instance;
    }
    
    // The big five. We don't want singleton instances to be
    // copyable nor movable. They should always be accessed with
    // ::instance.
    ~Singleton() = default;
    Singleton(Singleton&) = delete;
    Singleton(Singleton&&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    Singleton& operator=(const Singleton&&) = delete;
    
    void say_hello_world() {
        std::cout << "Hello world!" << std::endl;
    }

private:
    Singleton() = default;
};


int main()
{
    auto& inst = Singleton::instance();
    inst.say_hello_world();
}