Though professional software engineers are by definition well-equipped to handle a variety of software projects, abiding by software design principles ultimately optimizes the development process.
Naturally, there are numerous design principles that complement the development needs of any developer who would appreciate the guidance.
But there are a few software design principles that relatively every expert developer has hard-wired into their brains.
These principles stand out because they remain dependable, time and time again.
For a glimpse into the most valuable software design principles driving successful software development, keep reading.
DRY (Don’t Repeat Yourself)
The DRY principle seeks to reduce repetition in software programming to avoid redundancy.
It’s far too common for software engineers to have to write strikingly similar pieces of code over and over again.
Thankfully, the solution to this is by no means impractical. For example, object-oriented programming relies on classes to save bits of data into manipulable objects.
These objects can be called at any point in time and take on parameters that describe what the object works with or the extent of the object’s function.
Encapsulating code into objects depends on several other guiding principles, such as:
- Abstraction
- Pluggability
- Reusability
Abstraction refers to consolidating the complexity of a program element by hiding its internal details.
The code that exists in an object, for instance, is hidden from the user after its creation.
While working with data structures in Python, users can edit lists via various pre-built Python objects.
To append an item, they would use:
[list name].append(x)
Or to remove an item, they’d use:
[list name].remove(x)
In these examples, append() and remove() are object calls and x defines what list item the object should append or remove.
The Python user needs no prior understanding of the objects’ code to use these objects. They only need to name its attributes (parameters).
Naturally, this abstraction lends towards reusability and pluggability.
Objects and other program elements that implement DRY can be reused — effectively curtailing duplication — and you can plug them virtually anywhere in your program.
A modern example of DRY in practice would be Django Packages, a directory of apps and other resources built by Django contributors, and available to all Django users.
Ironically, a violation of the DRY principle is dubbed WET, or ‘waste everyone’s time.’ Likewise, AHA stands for ‘avoid hasty abstractions’, which leads to premature optimization.
YAGNI (You aren’t gonna need it.)
YAGNI asserts that programmers should only add functionality when absolutely necessary and never before.
The man behind this principle, Ron Jeffries, is also a co-founder of extreme programming (XP), a software development methodology and Agile framework.
The original words of Jeffries were, “Always implement things when you actually need them, never when you just foresee that you need them.”
Without a doubt, this should be a priority in a software methodology that intends to improve software quality by encouraging frequent releases on the basis of changing customer requirements.
The end goal in such methodologies is not only to deliver fast but to deliver satisfaction.
And it is easy to fall short on both these objectives when software engineers focus too much on adding every odd and end in sight.
YAGNI borrows from the XP principle DTSTTCPW or ‘do the simplest thing that could possibly work.’
And another important principle of software programming, continuous integration, plays into YAGNI as well.
Continuous integration (CI) is a software development practice where developers regularly merge code changes into a shared repository.
It goes without saying that major changes can result in disorganization down the line.
Overall, the gist of all these corresponding principles is that you save yourself the work of cleaning up a big mess when you just start simple and adjust accordingly.
Maintainability and clean code are the much-desired merits of any successful software project, meaning less generally serves best.
KISS (Keep It Simple, Stupid)
Although calling someone stupid is never a great approach, KISS still has a lot to offer.
KISS mirrors YAGNI pretty closely. The KISS principle states that programmers should keep each small piece of software as simple as possible and avoid unnecessary complexity.
Implementations of this principle are far-reaching. As early as 1960, the U.S. Navy propagated the principle to emphasize that systems work best if they are simple rather than complex.
In fact, evidence traces the origins of the principle to Kelly Johnson, a lead engineer at the Lockheed Skunk Works, an aerospace technology corporation that frequently works with the U.S. military.
Other variations of KISS include ‘Keep it short and simple’ or ‘Keep it simple and straightforward.’
As far as both YAGNI and KISS are concerned, there are a few software development strategies you can use the ensure simplicity, like loose coupling and cohesion.
Loose coupling is software development’s answer to tight coupling when program structures are so densely entangled that changes become difficult and time-consuming.
In loose coupling, developers program software with room for modularity in turn for interconnectivity.
As a result, an application’s features and functions operate independently and don’t malfunction when another application feature or function is compromised.
Cohesion might seem like the opposite of that sentiment, but low coupling and high cohesion actually work in tandem and makes for good software design.
High cohesion entails that everything in the module or class tie together and support its central purpose.
One software concept that illustrates both high cohesion and loose coupling is microservices.
Microservices consist of numerous services with each representing a single function or feature, that are bound together via APIs.
Services within this architecture should be highly cohesive as to be independently functional and self-contained. Yet, the coupling itself between services is low.
SOLID
SOLID principles are a combination of five software design principles, wrapped up in one aesthetically pleasing acronym. Here are those principles:
1. Single Responsibility Principle (SRP)
Classes define the behavior and data of objects, so developers can instantiate or call objects later in the program using a pre-defined class.
However, SRP maintains that a class should have one and only one reason to change.
This principle may seem cryptic but all it means is that a class should not have more than one responsibility.
In software, classes are the technical equivalent of, “You had one job.”
2. Open/Closed Principle (OCP)
OCP stresses that software entities should be open for extension but closed for modification.
In short, this specifies that adding new functionality should occur by extending existing functions, not changing them entirely.
When it comes to changing requirements, this principle makes the software development life cycle much more efficient.
3. Liskov Substitution Principle (LSP)
The Liskov Substitution principle holds that an object and its sub-object must be interchangeable without disrupting the program.
For the non-technically-savvy, this might seem like gibberish. For the technically savvy, this also might seem gibberish.
But think of it this way — every square is a rectangle, but not every rectangle is a square.
Apply this to software development, and you’ll find that giving every square object the properties of the rectangle class won’t make for the most accurate geometry.
4. Interface Segregation Principle (ISP)
The ISP is similar to the SRP in that it desires to mitigate the negative impact of frequent changes.
Except, the ISP does this by urging developers to split code into multiple, independent parts.
In particular, the principle states that many client-specific interfaces are better than one general-purpose interface.
Again, microservice vs. monolithic architecture models why this is true.
Developers favor microservices over monolithic architecture because although the latter is general-purpose, it necessitates excessive dependencies that further complicate the program.
5. Dependency Inversion Principle (DIP)
The Dependency Inversion principle makes multiple assertions:
- High-level modules should not depend upon low-level modules. Both should depend upon abstractions.
- Abstractions should not depend upon details. Details should depend upon abstractions.
In this case, such a principle emphasizes the importance of abstractions to induce low coupling.
In plain English, the principle suggests reducing dependencies by disentangling modules and abstracting details where you can.
Conclusion
The design principles you’ve seen here are instrumental to every programming endeavor. Make sure that these principles guide your next software project.
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