Introduction:
In software engineering, a programming design and architecture pattern is known as Singleton & Scoped. This pattern relates to the control of the instantiation process, which is primarily responsible for managing the creation of new objects. Singleton and Scoped are two of the most common instantiation patterns used by developers to achieve efficient, optimized, and reusable codes. This article aims to describe both patterns with code examples, benefits, and drawbacks. It will also answer some frequently asked questions about both patterns.
What is Singleton & Scoped?
“Singleton” and “Scoped” are the two most commonly used design patterns in programming. They are classified under instantiation patterns. Both patterns are different and serve different purposes, even though they both relate to the creation of objects.
The Singleton pattern restricts an object instantiation to only one instance. In other words, it ensures that only one instance of a class is created, and all objects refer to that single instance. This is done by making the constructor private, and providing a static method that returns the sole instance, which is created only once.
Scoped is a pattern that focuses on managing objects’ lifetime during their instantiation, depending on their scope or context. For instance, it is commonly used to manage resources or objects that depend on a shared context. When the context is no longer available, Scoped deletes the resources.
What is the difference between Singleton and Scoped?
The primary difference between Singleton and Scoped is that Singleton restricts object instantiation to a single instance and provides global access to it. Scoped, on the other hand, manages the creation and destruction of objects based on their context or scope.
Singleton and Scoped share some similarities, such as being used for controlling object instantiation in a program. However, they differ in their application and implementation.
When should you use Singleton?
Singleton is an excellent pattern to use when an object needs to be shared across multiple parts of your code, such as a global logger class that can track the logs for the entire program.
Here are some benefits of using Singleton:
– It restricts object creation to a single instance, ensuring shared access.
– It reduces the number of objects created, which optimizes resource utilization.
– It provides an easy-to-access instance globally with a static method.
– It increases the customization and flexibility of your program.
However, some drawbacks to keep in mind before implementing Singleton:
– Most singletons can only be created during the application’s launch, which might create a slower start time.
– It might lead to dependency injection issues because the singleton is so ingrained in the program’s structure.
– Multiple threads can interfere with the object’s unique property, leading to data corruption.
When should you use Scoped?
Scoped is an excellent choice when dealing with objects that have a specific lifetime management requirement. The most commonly used scenario is when managing resources such as file streams or database connections.
Here are some benefits of using Scoped:
– It ensures clean, predictable, and safe resource management.
– It reduces resource leaks by managing object lifecycles and memory allocation.
– It increases debugging and error handling by ensuring proper cleanup of the resources.
– It provides a way to manage context-specific objects.
Some drawbacks of Scoped:
– Not suited for objects that need to be shared or accessed globally.
– It tightly couples object destruction with scope or context, leading to a somewhat rigid programming paradigm.
– Object creation and management must be explicit, which can lead to more coding.
Code Example for Singleton:
Here is an example of a Singleton class pattern:
“`html
class Singleton {
private:
static Singleton* instance;
Singleton() {} // private constructor
public:
static Singleton* getInstance() {
if (instance == NULL) {
instance = new Singleton();
}
return instance;
}
};
Singleton* Singleton::instance = NULL;
int main() {
Singleton* s1 = Singleton::getInstance();
Singleton* s2 = Singleton::getInstance();
if (s1 == s2) {
cout << "Only one instance created." << endl;
}
return 0;
}
“`
Code Example for Scoped:
Here is an example of a Scoped class pattern:
“`html
class ScopedResource {
public:
ScopedResource() {
cout << "Resource created." << endl;
}
~ScopedResource() {
cout << "Resource destroyed." << endl;
}
};
int main() {
ScopedResource res1; // Resource Created
{
ScopedResource res2; // Resource Created
}
// Res2 destroyed
// Res1 destroyed
return 0;
}
“`
FAQs for Singleton and Scoped:
Q: Is Singleton considered an anti-pattern? A: Singleton is not necessarily an anti-pattern, but developers should consider the drawbacks that come with the pattern’s extensive use, such as increased coupling and possibly performance implications.
Q: Is Scoped the same thing as RAII?
A: Scoped is based on the RAII concept, which ensures the safe and controlled use and destruction of resources.
Q: Can Scoped manage dynamic memory allocation?
A: Yes, Scoped can manage d ynamic memory allocation, but the object lifetime management remains the responsibility of the developer to ensure resource safety.
Q: Can objects implementing Singleton be destroyed accidentally?
A: Since Singleton can only have one instance, objects implementing it are not destroyed until the whole program shuts down.
Conclusion:
Singleton and Scoped are essential patterns that help in managing object creation, destruction, and resource allocation in programs. Singleton is great for managing shared resources, while Scoped is perfect for managing resource lifetime. Both patterns have their benefits and drawbacks, and choosing which one to use depends on your project’s requirements. Understanding the differences between Singleton and Scoped is essential, and developers must consider these patterns’ consequences before implementing them in code.