Kotlin

---
name: kotlin patterns
description: Conventions for using Kotlin
---

## 1. Remove usage of `!!` operator

The `!!` operator should be avoided in Kotlin as it can lead to `NullPointerException` at runtime. Instead, use safe calls (`?.`) or the `let` scope function to handle nullable values more gracefully.

## 2. Remove the safe call operator (`?.`) when possible

Using the safe call operator (`?.`) is a good practice, but it should be used judiciously.
It makes no sense to use this operator when the value is guaranteed to be non-null, as it can lead to unnecessary null checks and reduce code readability.

## 3. Avoid using `var` when possible

In Kotlin, it is recommended to use `val` instead of `var` whenever possible. This helps to make the code more readable and maintainable, as it makes it clear that the value of a variable is not expected to change.

## 4. Use Duration overload when possible

### Example 1

When using the `delay` function, it is recommended to use the overload that accepts a `Duration` parameter instead of a `Long` parameter. This makes the code more readable and easier to understand, as it clearly indicates the intended duration of the delay.

replace this:

```kotlin
delay(100)
```

with this:

```kotlin
delay(100.milliseconds)
```

Add import: `import kotlin.time.Duration.Companion.milliseconds`

## 5. Remove all code signatures

Code does not need to be signed. The code signature used to have some value, but in current times, the commit already has a signature.
Old code may contain signatures that look like this:

```kotlin
/**
 * Created by joao on 28-4-16.
 */
```

They should all be removed, as they are not needed and add no value to the code.

## 6. When using Kotlin code make sure to use the kotlin extensions for parsing

### Example 1

When finding this:

```kotlin
    .getForEntity("/tulips", String::class.java)
```
replace with:
```kotlin
    .getForEntity<String>("/tulips")
```

## 7. Update the usage of `CSVParser` which is now deprecated

This skill refers to the `CSVParser` from `org.apache.commons.csv.*`

### Example 1

Replace
```kotlin
val csvParser = CSVParser(reader, CSV_HEADER)
```

with

```kotlin
val csvParser = CSVParser.builder()
    .setReader(reader)
    .setFormat(CSV_HEADER).get()
```

### Example 2

Replace this

```kotlin
private val CSV_HEADER = DEFAULT
    .withHeader(
        "id",
        "description",
        "year",
        "value",
        "currency",
        "type",
        "diameterMM",
        "internalDiameterMM",
        "heightMM",
        "widthMM"
    )
```

with:

```kotlin
private val CSV_HEADER = CSVFormat.DEFAULT.builder()
    .setHeader(
        "id",
        "description",
        "year",
        "value",
        "currency",
        "type",
        "diameterMM",
        "internalDiameterMM",
        "heightMM",
        "widthMM"
    ).get()
```

## 8. For all uses of Lombok in Kotlin classes that still use its builder pattern, please convert them to data classes

Due to Java conversions to Kotlin, some of them, due to their automatic nature, didn't consider the existence of data classes.
If Kotlin classes still use lombok for the builder pattern please convert them to `data class`.

## 9. Checklist

[ ] The code does not use the `!!` operator.
[ ] The code does not use the safe call operator (`?.`) when the value is guaranteed to be non-null.
[ ] The code uses `val` instead of `var` whenever possible.
[ ] The code uses the `Duration` overload when using the `delay` function.
[ ] The code does not contain any code signatures.
[ ] The code uses the kotlin extensions for parsing when using Kotlin code.
[ ] The code should not use the `CSVParser` constructuro directly