Tidy First?

Chapter 1. Guard Clauses

You see some code like this:

if (condition)
    ...some code...

Or even better, this:

if (condition)
    if (not other condition)
        ...some code...

As a reader, it’s easy to get lost in nested conditions. Tidy the above to:

if (not condition) return
if (other condition) return
...some code...

This is easier to read. It says, “Before we get into the details of the code, there are some preconditions we need to bear in mind.”

(But what about MuLTipLe ReTuRns? The “rule” about having a single return for a routine came from the days of FORTRAN, where a single routine could have multiple entry and exit points. It was nearly impossible to debug such code. You couldn’t tell what statements were executed. Code with guard clauses is easier to analyze because the preconditions are explicit.)

Don’t overdo guard clauses. A routine with seven or eight guard clauses (I’ve seen it in the wild) is not easier to read. It needs more acute care to partition complexity.

Only tidy to a guard clause if the prompt is met precisely:

if (condition)
    ...all the rest of the code in the routine...

I see code I want to tidy but can’t:

if (condition)
    ...some code...
...some other code...

Maybe the first two lines can be extracted to a helper method and then a guard clause tidied, but always and only take tiny steps.

Here’s an example: https://github.com/Bogdanp/dramatiq/pull/470.