Software design patterns are reusable solutions to commonly occurring problems in the software development world. These patterns provide a way for developers to structure their code in a consistent and organized manner, making it easier to write maintainable and scalable code. Design patterns provide a common language for developers to communicate and collaborate on software projects, helping to improve the overall quality of the code. They are also highly adaptable and can be applied to a wide range of programming languages and environments. Design patterns provide a blueprint for solving complex software development problems, and they have been widely adopted and used by developers for many years.
Some of these patterns provide solutions related to object creation (Creational), while others provide mechanisms for objects communication (Behavioral) and compositions (Structural). Creational design patterns include patterns which specify ways to instantiate class and objects, and they include factory method, abstract factory, singleton, builder and prototype.
This post will cover singleton design pattern including definition, use cases, benefits and drawbacks, and dart implementation. At the end of this post, you’ll have enough knowledge that’ll enable you to implement singleton at the right place and time.
Table of Contents
- What is the Singleton Design Pattern and how does it work
- When to use Singleton Design Pattern (Use Cases)
- How to Implement Singleton Pattern in Dart
- Benefits and limitation of the Singleton Design Pattern
- Conclusion
What is the Singleton Design Pattern and how does it work
According to the gang of four, Singleton is a design pattern that restricts the instantiation of a class to a single instance. It’s a creational design pattern that limits object’s instances to one, and provide a global access point to it. This means that a class has only one instance during the app’s lifecycle and this instance can be accessed anywhere within the app. There will be a single instance of this class no matter how many times the app requests an instance as it will always receive the same one.
The singleton pattern is often used in situations where there must be a single instance of a class that provides access to shared resources, such as a database connection or a configuration file. By limiting the number of instances of a class to one, the singleton pattern ensures that the shared resources are managed correctly and consistently throughout the application.
Analogy of Singleton Design Pattern
Think about a restaurant working team. There’s only one head chef, right? we’ll, that could be thought of as a singleton class whereas the restaurant is the application that requires access to the shared resources managed by the head chief. Just like the restaurant’s kitchen has one head chef who is responsible for managing and coordinating the preparation and cooking of all the dishes, the singleton class has only one instance that manages access to shared resources throughout the application. The shared resources could include things like ingredients, cooking utensils, and recipes.
The head chef is responsible for ensuring that the kitchen work efficiently and produce consistent high quality dishes. The same way, the singleton instance is responsible for ensuring that the shared resources are managed correctly and consistently throughout the application. Despite that there might be other chefs who assist the head chef in the kitchen , this head chef remains the point of authority no matter how many other chefs there are. And similarly, while there may be other methods s in the singleton class that assist with managing the shared resources, the singleton instance remains the single point of access to those resources.
How does Singleton Design Pattern Work
The singleton class has a private constructor to prevent creating additional instances from outside the class. This is impossible to be achieved using a normal constructor as it will always return a new instance of the object being created. In addition to the private constructor, the singleton class has also a static method which provides access to the single instance of the class. This method simply returns an instance of the class if it doesn’t already exist, or return the existing instance if it was already created.
One thing to keep in mind is that singleton pattern should be used carefully. This is because using this method randomly can lead to a tightly-coupled code and make testing somewhat difficult. In addition to that, developers assumes that singleton make code harder to maintain and negatively affect the app’s performance.
When to use Singleton Design Pattern (Use Cases)
As already mentioned, the singleton design pattern is mostly appropriate when there should be a single instance of a class which should also be globally accessible. Some of the common use cases of singleton includes:
- Resource management: this is the most common use case of singleton pattern as it’s used when you need to manage a shared resource such as database or file storage. In such cases, singleton ensures using the resource consistently and accurately throughout the application. Let’s say you have an application that uses database, singleton ensures that only one instance of the database is created, and it controls opening and closing the database connection. In addition to having the benefit of resource management, opening and closing the database connection only once saves memory which helps in improving the performance as these are heavy tasks.
- Application settings: This is when you need a single set of application-wide settings such as system configuration. You can create a singleton class which manages one set of settings rather than managing these settings from different classes. For example, you have one set of volume setting in an application, right? you don’t have a lower volume on a particular app screen while having a higher volume on another. Using singleton in such case ensures having a consistent settings and help simplify the code by having a centralized point of access to settings.
- Logging: This case is when you have an application that logs events and messages, you want them to be logged using a single log file. All your app modules would have access to this one and only log file.
Real-world Scenarios of Using Singleton Pattern
The singleton design pattern in already being used and you’ve probably come across it somehow if you’ve used Flutter enough. Take Firebase as an example. Firebase services, such as Firebase authentication, cloud storage and Firestore, use the singleton pattern to restrict the service instance to one. If you paid attention, Firebase services are always instantiated using the ‘instance’ keyword which is basically the singleton way of instantiating an object.
We’ve had enough theory, right? let’s jump into some coding and learn how to implement singleton in dart
How to Implement Singleton Pattern in Dart
class HeadChef {
//private constructor
HeadChef._();
//static method
static final instance = HeadChef._();
}
By creating a private constructor, we ensure that the class cannot be instantiated outside the file where it is defined.
Benefits and limitation of the Singleton Design Pattern
There are certain times when singleton is a perfect pattern to implement in applications. It’s recommended to use singleton wisely and only use it when it’s necessary. The benefits this pattern brings are invaluable but they don’t apply to every scenario so always consider it twice before approaching it. However, some of singleton’s benefits include:
- single class instance: Singleton limits the number of instance can be created to only one. Relating to Flutter, this can be beneficial when creating packages and libraries to restrict the number of instances that can be created by a single app.
- global access point: Singleton acts as a central point that can be accessed globally by different classes while ensuring that only a single version exists.
- consistent state: The Singleton Design Pattern ensures that there is only one instance of an object, which helps to maintain a consistent state of an object across the application.
- easy to change: since singleton pattern provides a centralized point of control for an object, making changes requires shorter time and can be done easier without affecting the rest of the app.
On the other hand, while the Singleton pattern can be useful in certain scenarios, it also has some potential drawbacks that you should be aware of:
- Global state & testing: this refers to the to the data that’s shared across the application and can be accessed anywhere in the app. This global state can make it difficult to isolate and test particular modules or parts as it can affect other parts of the app. For example, if the Singleton object is used to store configuration settings, changing its state could affect the behavior of other parts of the application that rely on those settings. Therefore, it’s important to carefully consider the use of the singleton design pattern and make sure it’s used appropriately.
- Performance: When an instance is created using the singleton class, it stays alive the whole time as long as the app is running. This means additional memory is required to keep this instance which can cause a poor performance.
- Hidden dependencies: With the Singleton Design Pattern, the instance of the Singleton object is globally accessible throughout the application. This means that any part of the application can access and modify the Singleton object, creating dependencies between different parts of the application. These hidden dependencies make code modification nearly impossible without affecting other parts that rely on this object.
- Tight coupling:When a singleton instance is used, other modules of the app may depend on it directly, creating a tight coupling between those modules and the instance created. This means that any modification made to the singleton object will affect those modules and potentially lead to bugs or unexpected behavior. Moreover, the singleton object could also be coupled on another singleton object or global variables making things even more complicated. This could lead to a chain of inter dependencies which can be very difficult to track and maintain.
Conclusion
The Singleton Design Pattern is a widely-used design pattern that provides a way to ensure that only one instance of a class is created and that this instance can be accessed globally within an application. This pattern can be used in different situations like controlling shared resources, logging, and setting configuration, and it’s already being used by different Flutter plugins such as Firebase. While it has various advantages, such as ensuring consistent state and single point of access, it is important to be aware of its drawbacks, such as tight coupling, poor performance, and global state.
Overall, the Singleton Design Pattern can be a powerful tool for improving the modularity and maintainability of applications, as long as it is used appropriately and with an understanding of its strengths and weaknesses.
When it comes to design patterns, it’s important to analyze each pattern and evaluate the best use cases for each of them. This helps you build a solid understanding of the role each plays which helps you decide which one to use based on your situation.
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