Singleton.h

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/**
 * @file Singleton.h
 * @author Gereon Kremer <gereon.kremer@cs.rwth-aachen.de>
 */
 
#pragma once
 
namespace carl
{
 
/**
 * Base class that implements a singleton.
 * 
 * A class that shall be a singleton can inherit from this class (the template argument being the class itself, see CRTP for this).
 * It takes care of
 * <ul>
 * <li>deleting the copy constructor and the assignment operator,</li>
 * <li>providing a protected default constructor and a virtual destructor and</li>
 * <li>providing getInstance() that returns the one single object of this type.</li>
 * </ul>
 */
template<typename T>
class Singleton
{
protected:
    /**
     * Protected default constructor.
     */
    Singleton() = default;
 
public:
    Singleton(const Singleton&) = delete;
    Singleton(Singleton&&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    Singleton& operator=(Singleton&&) = delete;
 
    /**
     * Virtual destructor.
    */
    virtual ~Singleton() noexcept = default;
    /**
     * Returns the single instance of this class by reference.
     * If there is no instance yet, a new one is created.
     */
    static T& getInstance() {
        static T t;
        return t;
    }
};
 
}