Many years ago, I took part in the development of a taxi-hailing mobile app that is still widely used today. I don’t know what kind of code they’re running now, but in those early days, the driver assignment code –if I remember it correctly– was similar in spirit to the grossly simplified example that follows. There are five levels of nested if statements in less than 30 lines of code. It doesn’t look so bad, some might say, but it’s not difficult to imagine how complicated this code can become with just a few more checks…
Looks like it’s JavaScript, but in Java I would prefer to use the Stream API, something like this:
return availableDrivers.stream() .filter(driver -> calculateDistance(rider, driver) < 5) .filter(driver -> isPreferredVehicle(rider, driver)) .filter(driver -> meetsRiderPreferences(rider, driver)) .findFirst() .orElse(null);
Then we have:
private boolean meetsRiderPreferences(Rider rider, Driver driver) { if (driver.rating >= 4.5) { if (rider.preferences.includes('Premium Driver')) { return driver.isPremiumDriver; } else { return true; } } else if (driver.rating >= 4.0) { return true; } else { return false; } }
This increases the separation of concern in a neat way, and it becomes more clear what the for loop does at a glance (get the first driver satisfying a set of conditions). The more complicated logic is isolated in meetsRiderPreferences, which now only returns true or false. Reading the method is more about making a mental map of a truth table.
It’s also easy to expand the logic (add more filter conditions, sort the drivers based on rating and distance, break out meetsRiderPreferences into smaller methods, etc.).
Not sure how the equivalent in JavaScript would look like, but this is what I would do in Java.