How can you improve software design with functions?

Functions are one of the most fundamental building blocks of software engineering. They allow you to write reusable, modular, and testable code that performs specific tasks. But how can you improve software design with functions? In this article, you will learn some principles and best practices to write better functions that enhance the quality, readability, and maintainability of your software.

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1 What is a function?

A function is a segment of code that takes some input, performs some logic, and returns some output. A function can be defined by a name, a list of parameters, and a body. For example, in Python, you can define a function that calculates the area of a circle as follows:

def area_of_circle(radius):
  pi = 3.14
  return pi * radius ** 2

You can then call the function by passing a value for the radius parameter and assign the result to a variable:

r = 5
a = area_of_circle(r)
print(a)

The output of this code is 78.5.

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Aron Kovacs

Principal Software Engineer, Consultant, Senior Software Architect with 15+ years of experience in IT.
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In my opinion a function is an enclosed functionality with well defined input and output criteria. What is really important here, to be able to define with your own words what a function does, by the name, parameters, etc.

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Jim Rogers

Senior Scientist, Senior Software Safety Engineer, Senior Software Engineer, Chemist
(edited)
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A function is one kind of a subprogram. A function may have parameters and always returns a value. A procedure may have parameters and never returns a value. Subprograms are used to encapsulate algorithms so that they may be conveniently reused in various parts of a program.

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2 Why use functions?

Functions have many advantages for software design, such as reducing code duplication and repetition, improving readability and clarity, facilitating modularity and abstraction, and enabling testing and debugging. Writing code in functions instead of multiple times allows you to call it whenever necessary. Descriptive names for functions make the code easier to understand for yourself and other developers. Additionally, functions can be organized into modules or libraries that group together related functionality. This separates different aspects of your software while hiding implementation details from the user interface or other components. Testing and debugging functions individually makes it easier to verify their correctness and performance, as well as locate and fix errors in your code.

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Aron Kovacs

Principal Software Engineer, Consultant, Senior Software Architect with 15+ years of experience in IT.
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Writing code without functions will be a hassle, jumping from point a to b, code repetitions, etc. Best way to start writing functions is to start to refactor an existing code, search for code parts with multiple occurences.

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Jim Rogers

Senior Scientist, Senior Software Safety Engineer, Senior Software Engineer, Chemist
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Functions greatly reduce duplication in a program. Write the function once and use it many times. The more often you write the same thing in your program the more chances you have of making a typing or logic error. If a function contains an error then you only need to fix that error in one place instead of fixing it in many repeated locations in your source code.

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3 How to write good functions?

Writing good functions is not only about syntax and style, but also involves following certain principles and best practices that can improve the design and quality of your code. To write good functions, it's important to keep them short and simple, with a clear and concise name that reflects its purpose. Additionally, make them pure and deterministic by avoiding side effects like modifying global variables or accessing external resources. When it comes to naming, use descriptive words that follow a consistent convention that matches the language and project standards. Finally, document and comment your functions by providing a docstring that explains what the function does, what parameters it takes, and what output it returns, as well as comments that explain any complex or unclear logic or assumptions in the function body. Doing this will help others understand and use your functions correctly and efficiently.

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Jim Rogers

Senior Scientist, Senior Software Safety Engineer, Senior Software Engineer, Chemist
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It is best if you write your functions using Design By Contract. Design By Contract employs preconditions, describing the requirements placed upon the function parameters, and post-conditions defining requirements placed on the function. Design By Contract creates interface requirements associated with the function so that both the programmer and the compiler understand how to interface with the function.

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4 How to refactor your functions?

Refactoring is the process of improving the design and structure of your code without changing its functionality. Doing so can help you enhance the quality, readability, and maintainability of your functions. To refactor, you can extract smaller functions from larger ones, combine similar functions into one, replace nested or recursive functions with loops, and replace magic numbers or strings with constants or variables. By doing this, you can make the code more modular, reusable, testable, readable, and maintainable. Additionally, it can also improve the performance of your code.

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Jim Rogers

Senior Scientist, Senior Software Safety Engineer, Senior Software Engineer, Chemist
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While refactoring a subprogram it is critical to maintain a consistent interface for the subprogram. This means, using Design By Contract, that the preconditions and post-conditions do not change.

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5 How to test your functions?

Testing is the process of verifying the correctness and performance of your code. It can help you ensure that functions work as expected and handle different scenarios and inputs. Common ways to test your functions include unit tests, integration tests, and manual tests. Unit tests are tests that check the functionality of a single function or module, while integration tests check the functionality of multiple functions or modules that work together. Manual tests are performed by running the software and interacting with it, allowing you to check the user interface, user experience, and usability of your software. Testing with these methods can detect and fix errors, bugs, and edge cases in your code, as well as verify and validate the overall functionality and performance of your software. By following these principles and best practices, you can improve software design with functions, creating better software that is reusable, modular, testable, and maintainable.

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Jim Rogers

Senior Scientist, Senior Software Safety Engineer, Senior Software Engineer, Chemist
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Subprograms are frequently tested using unit tests. It is also important to perform integration testing to ensure that your subprogram contracts are correct, consistent and honored by all the modules in your program.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How can you improve software design with functions?

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1 What is a function?

2 Why use functions?

3 How to write good functions?

4 How to refactor your functions?

5 How to test your functions?

6 Here’s what else to consider

Software Engineering

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