Design patterns are not strict rules or formulas; rather, they are guidelines that help developers to structure code in a particular way. Applying design patterns can streamline software development, making it more scalable, maintainable, and flexible.
Design patterns emerged in the field of computer science in the 1990s with the publication of the book "Design Patterns: Elements of Reusable Object-Oriented Software" by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides - sometimes referred to as the "Gang of Four". This book identified 23 commonly occurring patterns in object-oriented software development, such as the Singleton pattern, the Factory pattern, and the Observer pattern.
Since then, many more design patterns have been developed and applied across various programming languages and paradigms, including functional programming and reactive programming. Some common design patterns include creational patterns (e.g., Factory Method, Builder, and Abstract Factory), structural patterns (e.g., Adapter, Decorator, and Facade), and behavioral patterns (e.g., Observer, Strategy, and Visitor).
Design paterns can be very specific for a particular programming paradigm. We study design patterns to avoid reinventing the weel. If you know about common patterns you can search for code snipets or you can use AI to generate code for a specific language.
| Programming Paradigm | Design Pattern | Description |
|---|---|---|
| Object-Oriented Programming (OOP) | Factory Method | Creates objects without specifying the exact class to create. |
| Singleton | Ensures a class has only one instance, and provides a global point of access to it. | |
| Abstract Factory | Creates families of related objects without specifying their concrete classes. | |
| Builder | Separates the construction of a complex object from its representation. | |
| Prototype | Creates a new object by copying an existing object. | |
| Adapter | Allows two incompatible interfaces to work together. | |
| Bridge | Decouples an abstraction from its implementation. | |
| Facade | Provides a simplified interface to a complex subsystem. | |
| Functional Programming (FP) | Higher-Order Functions | Functions that can take functions as arguments and/or return functions as results. |
| Currying | Technique of transforming a function with multiple arguments into a sequence of functions with a single argument. | |
| Immutability | Provides a number of benefits, such as increased safety, performance, and concurrency. | |
| Reactive Programming | Observer | Objects that are notified when a subject's state changes. |
| Reactive Extensions (Rx) | Library for composing asynchronous and event-based programs by using observable sequences. | |
| Procedural Programming | Module | Encapsulates related functions and data into a reusable and maintainable unit of code. |
| Command | Encapsulates a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations. |
Design patterns are widely used in web development to solve common problems that occur when building web applications. These patterns provide proven solutions to common design problems and help developers avoid reinventing the wheel.
For example, the Model-View-Controller (MVC) pattern is commonly used in web development as a way to separate an application into three distinct components - the Model (data and business logic), View (user interface) and Controller (intermediary between Model and View). This separation provides better organization, maintainability, and flexibility, as each component can be modified independently.
Other design patterns such as the Front Controller, Decorator, and Repository patterns are also commonly used in web development to solve specific problems related to handling HTTP requests, modifying the behavior of objects at runtime, and centralizing data access.
The Model-View-Controller (MVC) pattern separates an application into three components:
MVC allows for better organization and maintainability of code.
The Single Page Application (SPA) pattern allows for faster and more responsive user experiences by loading content dynamically within a single web page. This avoids the traditional approach of loading a new page every time the user interacts with the application.
The Front Controller pattern consolidates all HTTP requests to a single point of control. This ensures that all requests go through a single component that can handle authentication, session management, and other common tasks.
The Decorator pattern allows for dynamic modification of an object's behavior at runtime by wrapping it with additional code. In HTML, this could be used to modify the behavior of an element by adding attributes or classes.
The Repository pattern provides a centralized location for accessing data in an application. In HTML, this could be implemented as a JavaScript object or array that holds data for the entire application.
Using design patterns in web development can lead to more structured, modular, and maintainable code, helping developers build high-quality applications with ease.
A design pattern for parallel computing is a repeatable solution to a common problem that arises when designing parallel applications. These patterns help designers structure their code to make the most of parallelism by identifying and exploiting the available parallelism in a computation.
| Design Pattern | Description |
|---|---|
| MapReduce | A programming model that divides input data into smaller chunks which are then processed independently and in parallel across a distributed network of processors or nodes. |
| Fork-Join | A parallel programming technique that involves breaking a larger task into smaller sub-tasks that can be parallelized, executing them in parallel, and then joining the results back together. |
| Pipeline | A design pattern that divides a larger task into stages, where each stage processes a subset of the data in parallel. The output of one stage becomes the input to the next stage until the final output is produced. |
| Master-Slave | A design pattern that involves a master node controlling a group of worker nodes or slaves. The master assigns tasks to the worker nodes, which then execute them and send the results back to the master. |
| Data Parallelism | A technique that involves dividing a data stream into smaller segments and distributing those segments across multiple processors. Each processor then performs an identical operation on its segment of the data, resulting in a parallel computation. |
| Bulk Synchronous Parallel (BSP) | A parallel computing model that involves dividing a computational problem into smaller chunks or supersteps, which are then executed in parallel by a set of processors. Each superstep consists of computations on local data in each processor followed by global communication among processors to synchronize results. |
By using patterns, designers can improve the efficiency, scalability, and maintainability of their parallel programs. By understanding and applying these patterns, programmers can create faster, more efficient, and more scalable parallel programs.
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