Analysis of the benefits of using singleton pattern design in CI framework

In the process of using the CI framework, you will find that the $ci super variable is passed by reference and value. What you obtain through get_instance() is always the same CI object.

Let’s introduce the benefits of doing this:

The singleton pattern is regarded as the responsibility pattern, which is used to create a single functional access point in the application.

It delegates control of creating objects to a single access point. At any time, only one instance of this class will exist in the application.
This prevents us from opening multiple connections to the database or using unnecessary system resources.
In more complex systems, using the singleton pattern is also particularly useful in maintaining synchronization of application state.

All singleton classes have at least the following three public elements: They must have a constructor and must be marked private. They have a static member variable that holds an instance of the class.

They have a public static method to access this instance. Different from ordinary classes:

Singleton classes cannot be instantiated directly in other classes. A singleton class can only be instantiated by itself.
To obtain such a result, the __construct() method must be marked as private. If you try to construct a class with a private constructor, you will get an accessibility level error.

For a singleton class to work, it must provide an instance for other classes and use it to call various methods.
The singleton class will not create a copy of the instance, but will return a reference to the instance stored inside the singleton class.
The result is that the singleton class does not repeatedly occupy memory and system resources, allowing other parts of the application to better use these resources.
As part of this pattern, an empty private __clone() method must be created to prevent the object from being copied or cloned. This method that returns an instance reference is usually named getTnstance(). This method must be static and must be instantiated if it is not already instantiated.

The getInstance() method can detect whether a class has been instantiated by using the instanceof operator and the self keyword.

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