Published in 2008, and over recent years, it has consistently ranked as one of the top five highest-selling books on Amazon. The author, affectionately known as “Uncle Bob,” was one of the original authors of the Agile Manifesto and has some serious credentials. The book has achieved an average rating of 4.4 on Goodreads from over 13,000 ratings. Suffice to say, it’s one of those books every programmer should read.
1. Programming is a craft.
But how do we go from simply writing code to crafting code?
According to Martin, the main tools we have at our disposal are continuous refactoring and test-driven development (TDD). These work together like two sides of a coin. Here are some definitions:
Refactoring is the process of restructuring existing computer code without changing its external behavior.
Test-driven development is a process where requirements are turned into specific test cases, then the code is added so the tests pass.
So, the process of crafting software might look something like this:
- Write failing tests that verify the required but unimplemented behaviour.
- Write some (potentially bad) code that works and makes those tests pass.
- Incrementally refactor the code, with the tests continuing to pass, making it more clean with each development iteration.
2. Keep it short!
According to Martin this means two things:
- Function bodies should be short — hardly ever longer than 20 lines and mostly less than 10 lines
- Functions should take as few arguments as possible, preferably none
Function brevity makes code easier to read. It also steers us towards a situation where functions do one thing — and do it well.
He makes a similar point about classes. With classes, he suggests using responsibilities as the measure of size rather than lines of code. The idea is a class should only be responsible for one thing. This is known as the single responsibility principle (SRP).
Keeping entities short is a divide-and-conquer strategy for making code cleaner. If we have a big file with lots of lengthy, complicated code, we can divide that file into modules, divide the modules into functions, and divide functions into subfunctions until the logic and intent are clear.
3. Make code self-documenting.
In
the sections on comments, meaningful names, and formatting, Martin
makes a strong case for code being self-documenting. An example of this
is given as follows:
// Check to see if the employee is eligible for full benefits
if ((employee.flags & HOURLY_FLAG) &&
(employee.age > 65))This gets refactored to
if (employee.isEligibleForFullBenefits())Note:
- The comment is removed
- The conditional logic is encapsulated into a method
- Because a method is used and not a free-standing function, instance variables can be used, creating a zero-argument method call
- The method is given a descriptive name, making its responsibility super clear
There's a full chapter on naming, which is essentially an elaboration on Tim Ottinger’s rules. These include:
- Use intention-revealing names — e.g,
int elapsedTimeInDays, notint days - Use pronounceable names — e.g.,
Customer, notDtaRcrd102 - Avoid encodings — don’t use an
m_prefix for members and don’t use Hungarian notation - Pick one word per concept — don’t
fetch,retrieve,getfor the same concept
4. Respect abstraction.
If we want to make sure our functions are only doing one thing, we need to make sure the statements within each function are all at the same level of abstraction.
public String render() throws Exception
{
StringBuffer html = new StringBuffer("<hr");
if (size > 0)
html.append(" size="").append(size + 1).append("\"");
html.append(">");
return html.toString();
}This is refactored to
public String render() throws Exception
{
HtmlTag hr = new HtmlTag("hr");
if (extraDashes > 0)
hr.addAttribute("size", hrSize(extraDahses));
return hr.html();
}
private String hrSize(int height)
{
int hrSize = height + 1;
return String.format("%d", hrSize);
}Notes:
- The
render()function is now only responsible for constructing anhrtag - The low-level details of constructing the tag are now delegated to the
HtmlTagmodule - Size formatting is abstracted into a separate function
5. Clean code is about principles and hard work.
“Clean code is not written by following a set of rules. You don’t become a software craftsman by learning a list of heuristics. Professionalism and craftsmanship come from values that drive disciplines.” — Robert C. Martin
*https://medium.com/better-programming/clean-code-5-essential-takeaways-2a0b17ccd05c
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