The Art of Readable Code

Chapter 7. Making Control Flow Easy to Read

If code had no conditionals, loops, or any other control flow statements, it would be very easy to read. These jumps and branches are the hard stuff, where code can get confusing quickly. This chapter is about making the control flow in your code easy to read.

Key Idea

Make all your conditionals, loops, and other changes to control flow as “natural” as possible—written in a way that doesn’t make the reader stop and reread your code.

The Order of Arguments in Conditionals

Which of these two pieces of code is more readable:

if (length >= 10)

or

if (10 <= length)

To most programmers, the first is much more readable. But what about the next two:

while (bytes_received < bytes_expected)

or

while (bytes_expected > bytes_received)

Again, the first version is more readable. But why? What’s the general rule? How do you decide whether it’s better to write a < b or b > a?

Here’s a guideline we’ve found useful:

Left-hand side	Right-hand side
The expression “being interrogated,” whose value is more in flux.	The expression being compared against, whose value is more constant.

This guideline matches English usage—it’s pretty natural to say, “if you make at least $100K/year” or “if you are at least 18 years old.” It’s unnatural to say, “if 18 years is less than or equal to your age.”

This explains why while (bytes_received < bytes_expected) ...