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Class __SingletonObject is not be instantiated

I would point out a couple issues of semantics and terminology.

• It's confusing to have a method named fly that can be implemented as not flying. Naming the method tryToFly or documenting the method as merely an attempt are two ways of addressing this confusion. The software principle to reference here is Liskov Substitution.
• The base class does not implement one of the strategies; rather, it composes a strategy. The purpose of the Strategy pattern is to avoid subclassing through composition.
• To reiterate one of the comments, Duck should accept an instance of IFly directly in its constructor (or a setter method) rather than switching on an enum. Another goal of the Strategy pattern is to avoid branching logic.

The essence of the pattern is that you've avoided creating multiple subclasses of Duck by instead creating multiple implementations of IFly. This has the advantage that those IFly implementations can be reused without a complex inheritance hierarchy, e.g. WILD and CITY can share one strategy.

As mentioned in the comments, strategies also have the advantage that a Duck could change its strategy at runtime. For example, IFly might be implemented by Soar and Glide so that a Duck would switch between these different strategies depending on the wind.

I found the answer:

I was excuting my test with this command line:

I bypassed the problem by removing the implementation of the UserDetails interface from my User entity, and set up a new mechanism to recover the GrantedAuthority necessary for Spring Security. But I still do not understand why this interface implementation poses a problem with setPackagesToScan used by the JPA EntityManagerFactory.

If somone can give us an explanation?

Is this due to the old version of G++ shipped by Apple?

No. It is because you are trying to copy the unique pointer by passing it to make_pair and insert.

std::unique_ptr is not copyable. In fact it is move-only. Change to:

I'd follow the XP rule of doing the simplest thing that could possibly work. You don't need to mock anything, so just use the objects directly.

Don't try and make a global variable accessible through all your code. Make a certain object accessible only to who needs it. Thus, make a private ShapeManager in Shape and pass it through Shapes constructor.

But it's still strange that Shape has to have access to ShapeManager.

EDIT - Comment by the author: My main motivation to creating a ShapeManager is to store a reference to m_shapes, m_world, and m_gen, but i didn't want every shape object to have those 3 reference variables.

You can have a struct that stores your 3 reference variables and each object that needs access to them would have a private struct.

Some other file:

PizzaStore class already contains a SimplePizzaFactory object

Well, PizzaStore have a non-initialized attribute of type SimplePizzaFactory. In the PizzaStore constructor, that attribute is initialized with a reference to the constructor argument. This is an usual pattern in Java code.

The passed-on object is not initialized with any data (which needs to be copied by PizzaStore Constructor)

There is no need to add initialization code in the constructor, is asumed that the SimplePizzaFactory is already initialized. That factory is not copied, is referenced by the PizzaStore attribute, so the factory inside the PizzaStore, after the constructor is executed, is an already initialized object.

What you need to do is to mock Item as well.