step-by-step.md

Day 3: One dot per line.

As a human being, how could it be possible to understand this code? We read vertically and here everything is positioned horizontally...

@Test
void whoOwnsTheYoungestPet() {
    var filtered = population.stream().min(Comparator.comparingInt(person -> person.pets().stream().mapToInt(Pet::age).min().orElse(Integer.MAX_VALUE))).orElse(null);

    assert filtered != null;
    assertThat(filtered.firstName()).isEqualTo("Lois");
}

We want to enforce the 1 dot per line rule because:

• High cognitive load to understand the code
• No IDE support
• Hard to understand what is changed from our git log

Let's start by improving the code by simply add some return lines

• It is already simpler to understand...

• Now our IDE is able to provide us some help by displaying return types on lines

• How could we go further?
  • We still have several dot per lines
  • Let's use Extract Method

• Our code now looks like this

@Test
void whoOwnsTheYoungestPet() {
    var filtered = population.stream()
            .min(comparingInt(PopulationTests::youngestPetAgeOfThePerson))
            .orElse(null);

    assert filtered != null;
    assertThat(filtered.firstName()).isEqualTo("Lois");
}

private static int youngestPetAgeOfThePerson(Person person) {
    return person.pets()
            .stream()
            .mapToInt(Pet::age)
            .min()
            .orElse(Integer.MAX_VALUE);
}

• We could go further by putting the behaviors closer to the business logic to respect the law of Demeter
  • Moving the youngestPetAgeOfThePerson method in Person for example

Vavr alternative

By using, alternative collections the code could be a little bit less verbose...

Take a look at it :

@Test
void whoOwnsTheYoungestPet() {
    assertThat(population
            .minBy(PopulationWithVavrTests::youngestPetAgeOfThePerson)
            .get()
            .firstName()
    ).isEqualTo("Lois");
}

private static int youngestPetAgeOfThePerson(Person p) {
    // List.ofAll(p.pets()) is needed here, just to convert java list to vavr list
    return List.ofAll(p.pets())
            .map(Pet::age)
            .min()
            .getOrElse(MAX_VALUE);
}

Promyze

Promyze is a platform with the below promise:

Help you build always up-to-date coding standards that your team can learn from, making them actionnable in the IDE and during PRs.

As a team, we may define this kind of rules and use Promyze to detect this guideline during coding.

• In the platform we can define the Practice

• Configure the tool to detect in real time during coding (with regex)

Here is the regex used ^[^\n]*\.[^\n]*\.[^\n]*$.

• Once done, the suggestions appear (a rocket on the line)

• In our IDE, we can see the details directly

• The suggestions do not appear after our refactoring 🤩