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…
  • magic_lobster_party@fedia.io
    15·
    9 hours ago

    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.

    • Kissaki@programming.devEnglish
      51·
      6 hours ago

      Using early returns and ternary conditional operator changes

      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;
    }
}

      to

      private boolean meetsRiderPreferences(Rider rider, Driver driver) {
    if (driver.rating < 4.0) return false;
    if (driver.rating < 4.5) return true;

    return rider.preferences.includes('Premium Driver') ? driver.isPremiumDriver : true;
}

      dunno if java has them, but in C# switch expressions could put more of a case focus on the cases

      private boolean meetsRiderPreferences(Rider rider, Driver driver) {
    return driver.rating switch {
        < 4.0 => false,
        < 4.5 => true,
        _      => rider.preferences.includes('Premium Driver') ? driver.isPremiumDriver : true,
    };
}

      or with a body expression

      private boolean meetsRiderPreferences(Rider rider, Driver driver) => driver.rating switch {
    < 4.0 => false,
    < 4.5 => true,
    _      => rider.preferences.includes('Premium Driver') ? driver.isPremiumDriver : true,
};

      The conditional has a true result so it can be converted to a simple bool condition as well.

      private boolean meetsRiderPreferences(Rider rider, Driver driver) => driver.rating switch {
    < 4.0 => false,
    < 4.5 => true,
    _      => !rider.preferences.includes('Premium Driver') || driver.isPremiumDriver,
};
    • MagicShel@programming.dev
      5·
      9 hours ago

      I try to prefer .findAny() over .findFirst() because it will perform better in some cases (it will have to resolve whether they are other matches and which one is actually first before they can terminate - more relevant for parallel streams I think. findAny short circuits that) but otherwise I like the first. I’d probably go with some sort of composed predicate for the second, to be able to easily add new criteria. But I could be over engineering.

      I mostly just posted because I think not enough people are aware of the reasons to use findAny as a default unless findFirst is needed.

      • magic_lobster_party@fedia.io
        6·
        9 hours ago

        For me I have the habit of doing findFirst because determinism is important where I work. But I agree with you if determinism is not of importance.