Design patterns are a standard part of software engineering these days, yet remain one of the most misunderstood elements of the discipline. A developer's initial exposure to them is often as a collection of recipes, or a suite of code snippets to be copied and pasted faithfully. Applying design patterns as sacrosanct solutions does not help developers, their code, or their teams. We are more than widget makers, and we capable of much more than putting Tab A into Slot B. At their core, design patterns are a rather simple yet often unspoken truth about programming taken to a new level: fundamentally, programming is communication.
When we program, we simultaneously write a description of a system that is intended for two very different audiences: the compiler, and other developers. The compiler is happy as long as we strictly follow a language specification. Other developers, including our future selves, tend to be a little more demanding. We've all looked at a piece of code that we wrote months or years before, trying to reconstruct our reasoning. Developers want and need to know not only the what of the functionality, but also the why of the design. They want to know what is robust, and what is fragile. They want to know what is malleable, and what is behind an invisible line that they shouldn't touch. Developers need more information than the compiler.
Documentation is one way to provide this information, but in most environments it tends to quickly get out of sync with the source code. Immediate pressures such as shipping dates or clients' deadlines take priority over longer-term goals such as the robustness of the product. Design patterns, on the other hand, are woven into the source code itself, and cannot be out of sync. To a developer trained in their meaning, they offer a wealth of information above and beyond a functional description.
Design patterns are the distillation of the experience of many others into a tribal wisdom, and learning them can greatly increase your communication capabilities with other developers. They provide shared vocabulary, semantics, and documentation for concepts and design issues that stand outside the strictly computational aspects of our field.
Patterns can be difficult to gain experience with in the field, however. The existence of design patterns is often not as explicitly obvious in the code as say, the definition of an algorithm, and design patterns describe situations and solutions that may be outside a developer's current knowledge set. Until a developer has an intimate understanding of why certain problems exist, grasping why a particular solution is considered a best practice can be difficult. That understanding in turn takes experience, leading to a bit of a catch-22.
A book such as Elemental Design Patterns can help you learn the design patterns literature from the ground up. Elemental Design Patterns starts with the basic concepts that you use every day, and illustrates the core of programming in terms of patterns. This then becomes a springboard to dive into the literature and gain a deeper understanding of the hard-won experiences gathered there. Ultimately, you will be able to create robust and flexible systems more rapidly, and you will be a better communicator of your intentions, particularly of the more subtle points of your implementations and designs. As you work with developers similarly cognizant in design patterns, you will find that you more quickly comprehend their code as well.
Communication is enhanced because design patterns facilitate between developers the same traits that are needed for any effective information transfer. The informal "Seven C's of Effective Communication" are frequently referred to in careers where direct human-to-human communication is critical, such as management, marketing, and sales. There are various versions of this list floating about but they generally include some common themes including, in no particular order, Clarity, Conciseness, Consistency, Correctness, Completeness, Concreteness, and Courtesy. Again leveraging the idea of learning from the experiences of others, we can blatantly borrow these ideas and demonstrate how design patterns fulfill these same goals of effective communication.
Clarity of code is not determined by whether braces are placed on the next line, or an indentation style. Pulling off a well-timed clever hack to save the day can give a developer a fantastic feeling of accomplishment. Producing obfuscated code on a regular basis, however, is rather like a strong body check in ice hockey: a highly useful skill in a pressure situation, but if you do it to your colleagues out of the blue during an average day, you're just being a jerk. Code needs to be clear in what it does, and how it does it. Selection of meaningful names for variables, functions, and types is a start, but the overall design needs to also be quickly understandable. Design patterns give a developer insights into how to name and structure solutions so that they are readily identifiable to others by providing semantic cues both in clear naming, and obvious design constructs.
When you use design patterns, you can be concise in your expression. Instead of having to provide documentation to explain the background of why you chose to solve a problem in a particular way, how you expect it to be used and not be used, and so on, you can refer to the underlying design pattern directly. Even better, if you can use identifiable mnemonics of the design pattern in the code itself, you don't even have to produce documentation. The pattern you are using will be clear, and a developer reading your code can research that pattern only if necessary. Less for you to write, less for others to read. Everybody wins.
Whether you are working on a word processor or the control system for a fighter jet, a Singleton is a Singleton. Whether you are working in Java, C++, or Python, a Decorator is a Decorator. Implementations will vary, but the concepts and driving forces behind them remain the same. Design patterns transcend domains and languages, giving us a consistent terminology and comprehension. Not only will your current system benefit from consistent idioms, you will find yourself much more flexible in your career options because much more of your knowledge and experience can be transferred to different situations, programming languages, and programming environments.
Creating the correct solution for a given problem is not always trivial or obvious. Any programming problem can be solved in a nearly infinite number of ways. Very few of those implementations are good solutions, and even fewer are appropriate solutions. The design patterns literature works as an interconnected reference of related best-practice solutions. If it looks like one pattern will work for you, but you're thrown a curve ball that makes it no longer adequate or appropriate, the design pattern write up will refer you to related patterns, letting you select the best fit.
Using a design pattern as a guide for solving a problem also helps ensure that you are producing not just the correct solution, but the correct solution correctly. All too often, we solve problems in ways that look fine initially, but miss boundary cases and minute details that come back to bite us later. The collective wisdom found in design patterns bears the scars of many such bites. Design patterns have been battle-tested and determined to be best practice solutions that have stood the test of time. Incorrect solutions don't last long in such an environment.
Completeness goes hand in hand with correctness. Have you found all those boundary cases? Have you considered what will happen in two years when your requirements change but this code is still in use? Have you thought about all those little details that seem to pop up later, or are you going to have to engage in a game of whack-a-bug to keep the system running? How complete is your conceptual coverage? Learn from those that have come before you, who have found the cracks and gaps, and found proper ways to avoid or fill them. By utilizing design patterns, other developers can have increased trust in your solution's completeness and correctness.
When we produce a solution that our colleagues have not seen before, there is often a good amount of healthy skepticism. When we are in the process of creating a new solution, there is often a good amount of uncertainty within ourselves. In both cases, concrete examples and known parameters of design are a help in defining the problem and the solution. Referring to an existing specification and description not only spurs discussion, but also often highlights constraints that were not recognized or foreseen. Using design patterns in your discussions and coding offers a link to a wide body of such concrete information. Implementing a design pattern in your code and making it clear which pattern you are using also beautifully reduces the questions a later developer may have.
Finally, and getting back to the point above about obfuscated code being an assault on your colleagues, effective communication is simply courteous. When you write code that requires your teammates to spend time reconstructing your thinking in fine detail just to use or maintain your code, you are telling them that their time is worth little to you. Design and write your systems as if you are the one who will have to figure it out down the road, because chances are you will be. Design patterns are an aide in this process, letting you use a convenient shared shorthand for sometimes esoteric concepts that would require significant time and effort for your colleagues to ferret out. It is in everyone's best interest if your code communicates as effectively as it can.
In the end, programming is about effective communication. Until we can manage to achieve telepathy, there is no silver bullet to make communication between developers perfect, but we can use tools such as design patterns to make the task easier on many axes. On the compiler communication front, tool support for design patterns continues to improve. Support exists for the application of patterns to an implementation, and exciting advances are coming in the automated detection of patterns for code comprehension and enforcement of design compliance. Design patterns are a communication tool that we all can use collectively to create a better community for ourselves, and our clients. As our communication becomes more effective, so do our products, our systems, and our discipline. Use design patterns to catalyze the Seven C's for your own effective communication, and it could be you thanking yourself for creating a clear, courteous system. The rest of us certainly will.