kotlinlang #codingconventions

I think I started overusing trailing commas in Kotlin using them wherever I might benefit from shorter diffs in the future. What are your rules to limit trailing commas, keeping codebase clean?

Ellen Spertus

02/17/2021, 9:26 PM

Which do you like better? 1️⃣

boxes.forEach {
    it.setOnClickListener { 
        makeColored(it) 
    }
}

2️⃣

boxes.forEach { it.setOnClickListener { makeColored(it) } }

3️⃣ @Marc Knaup

boxes.forEach { it.setOnClickListener(::makeColored) }

4️⃣ @ephemient

for (box in boxes) {
    box.setOnClickListener { makeColored(it) }
}

5️⃣ @Marc Knaup @ephemient

for (box in boxes) {
    box.setOnClickListener(::makeColored)
}

1️⃣ 1

3️⃣ 17

5️⃣ 8

arekolek

03/04/2021, 1:57 PM

listOf(1, 2, 3).map { Unit }

IDE marks

Unit

as redundant and proposes to replace it with:

listOf(1, 2, 3).map { }

How do you handle this? Proposed fix looks weird to me. This issue occurs quite often in RxJava streams

diego-gomez-olvera

03/05/2021, 1:33 PM

I find the trailing commas convenient for the multi-line declarations, but also a bit strange on method calls. I wonder if they are commonly used (👍 for yes, 👎 for no), and in which cases https://twitter.com/dankim/status/1367602098985201671

👍 13

👎 2

Shawn

03/05/2021, 4:10 PM

I’ve literally never understood this.

val foo = Foo(
    bar,
    baz,
    qux
)

“so readable” “looks right” “as god intended”

val foo = Foo(
    bar,
    baz,
    qux,
)

“ew gross” “_literally_ unreadable” “`parse error: Expected another key-value pair`”

😆 6

miqbaldc

04/02/2021, 5:50 AM

any suggestion to improves below code?

data class State(title: String, description: String)

fun State.toSessionExpired(): State {
    val state = this
    return with(state) {
        // when token expired
        if (httpCode == 401) {
           copy(
               title = getString(R.string.error_expired_title),
               description = getString(R.string.error_expired_description),
           )
        } else this
   }
}

therealbluepandabear

04/09/2021, 5:40 AM

First or second:

val notificationHelper: INotificationHelper = NotificationHelper(this)
val notificationHelperTwo = NotificationHelper(this)

2️⃣ 6

therealbluepandabear

04/11/2021, 11:36 PM

First or second?

startActivityForResult(
    CheatActivity.newIntent(this@MainActivity, quizViewModel.currentQuestionAnswer),
    REQUEST_CODE_CHEAT,
    ActivityOptions.makeCustomAnimation(
        this,
        R.anim.fragment_fade_enter,
        R.anim.fragment_fade_exit
    ).toBundle()
)

val intent = CheatActivity.newIntent(this@MainActivity, quizViewModel.currentQuestionAnswer)
val animation = ActivityOptions.makeCustomAnimation(this, R.anim.fragment_fade_enter, R.anim.fragment_fade_exit).toBundle()
startActivityForResult(intent, REQUEST_CODE_CHEAT, animation)

Mark

04/12/2021, 2:27 AM

When declaring a higher order function (that accepts a lambda as argument) where you don’t use (and don’t care about) the return value of the lambda, do you put

Any?

Unit

for the return type? I guess

Any?

is the appropriate type, but I wonder if it adds confusion for example in private functions where you know the return type of the lambda is always

Unit

. 1.

Any?

always 2.

Unit

always 3.

Any?

when public,

Unit

when private and possible

2️⃣ 6

Matteo Mirk

04/20/2021, 3:00 PM

When translating a class’ static factory methods from Java (used to construct its instances, not the Factory pattern), what do you prefer to use and why? 1️⃣ companion object 2️⃣ top-level function At first [1] seems a direct translation and will be familiar to Java devs, while [2] gives the possibility to escape the class definition and even the same file (although extension function offer the latter benefit as well). What do you think feels more idiomatic Kotlin?

2️⃣ 2

1️⃣ 1

Tomasz Krakowiak

04/21/2021, 4:59 PM

When designing a API, what principles should I follow to choose whether given type should be SAM or typealias for a function type?

marcinmoskala

04/29/2021, 5:42 AM

When do you use fun interface instead of function type?

Ellen Spertus

05/04/2021, 5:27 PM

For an article I'm writing, could you tell me which version of the following code you would write/recommend? Feel free to add options. 1️⃣ if (b == true)
2️⃣ if (b == true) // b could be null
3️⃣ if (b != null && b)

1️⃣ 2

2️⃣ 2

christophsturm

05/05/2021, 2:29 PM

is the official kotlin code style really no star imports?

arekolek

05/10/2021, 7:20 PM

1️⃣

fun foo(bar: Bar) {
  if (!bar.canFoo) {
    <http://logger.info|logger.info>("No foo for this bar")
    return
  }
  // Make foo with bar
}

2️⃣

fun foo(bar: Bar) {
  if (!bar.canFoo) {
    return <http://logger.info|logger.info>("No foo for this bar")
  }
  // Make foo with bar
}

2️⃣ 1

1️⃣ 12

Mark

05/13/2021, 2:40 PM

Is it standard practice to name a

fun interface

as a verb when the function is

invoke

? Or maybe as a noun like here:

fun interface ItemSelector {
    operator fun invoke(items: List<String>): String
}

val selectItem = object : ItemSelector { ... }
val itemSelected = selectItem( ... )

1. Verb 2. Noun

marcinmoskala

05/14/2021, 8:17 AM

Based on the discussions here (1, 2), on Twitter, and my own experience, I tried to extract the general suggestions when to prefer function type and when functional interface. What do you think? Happy to see all kinds of suggestions and comments. (the article is not yet published, this is a preview) (tl;dr in the Summary) https://kt.academy/article/ek-function-types

👍 1

Sam

05/23/2021, 7:19 AM

Hello Good morning Im curious about 2 solutions convert

dp

px

Solution 1:

fun Int.dpToPx(context: Context): Int {
    return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, this.toFloat(), context.resources.displayMetrics).toInt()
}

Solution 2:

fun Int.dpToPx() = (Resources.getSystem().displayMetrics.density * this + 0.5f)

so Which once is correct for multiple screen? Thanks.

Marc Knaup

06/04/2021, 3:05 PM

How do you name factory functions? 1️⃣ Simple function name

fun interface SomeLongTypeNameFactory {
   fun create(): SomeLongTypeName
}

Con: Causes conflict if a class implements multiple factories. 2️⃣ Function name explicitly mentions type

fun interface SomeLongTypeNameFactory {
   fun createSomeLongTypeName(): SomeLongTypeName
}

Con: Long & repetitive. 3️⃣ Other convention (add comment)

3️⃣ 1

2️⃣ 2

1️⃣ 5

Chris

06/09/2021, 4:50 PM

Which would you choose / use? 1️⃣

it.toString()

or 2️⃣

"$it"

or 3️⃣ something else? Is 1️⃣ and 2️⃣ equivalent?

:yes: 2

1️⃣ 10

Victor Cardona

06/10/2021, 11:54 AM

I have a question after reading the coding conventions. It says to not separate extension methods from regular methods. So should I take that to mean that private extension methods should be within the class that makes use of them? I assume this would also apply to properties? For instance:

class A {
    fun doSomething(): Unit {
        ...
    }

    private val B.things: List<Thing>
        get() = ...

    private fun C.helpMe(): Thing { ... }
}

I currently have the extensions at the top-level, but from reading the guidance it sounds like I should move them into the class itself.

miqbaldc

06/17/2021, 10:59 PM

which one do you prefer/recommend or maybe another alternative options to suggest? 1️⃣

private fun AccountInfo?.isNotEmpty() = this != null && 
    id.isNullOrBlank().not() && 
    status.isNullOrBlank().not() &&
    something.isNullOrBlank().not()

2️⃣

private fun AccountInfo?.isNotEmpty() = this != null 
    && id.isNullOrBlank().not() 
    && status.isNullOrBlank().not()
    && something.isNullOrBlank().not()

3️⃣ (linter will complain when exceeded the max length)

private fun AccountInfo?.isNotEmpty() = this != null && id.isNullOrBlank().not() && status.isNullOrBlank().not() && something.isNullOrBlank().not()

2️⃣ 4

1️⃣ 1

miqbaldc

06/18/2021, 6:28 AM

any other alternative to suggest on below snippet code? 1️⃣

fun doSomething(): String {
  return if 
    aMethodHere1()
  else
    aMethodHere2()
}

2️⃣

fun doSomething(): String {
  return if aMethodHere1()
  else aMethodHere2()
}

3️⃣

fun doSomething(): String {
  return if aMethodHere1() else aMethodHere2()
}

1️⃣ 1

3️⃣ 1

Mark

06/22/2021, 3:35 AM

Often I’m faced with a choice of declaring a private function in a companion object (good for encapsulation) or at the top file level (reduces indentation). Which do you prefer?

class Foo {
    companion object {
        private fun bar1() { ... }
    }
}

private fun bar2() { ... }

private fun Foo.Companion.bar3() { ... }

1️⃣ companion object 2️⃣ top-level (file) 3️⃣ top-level companion extension

2️⃣ 7

4️⃣ 1

miqbaldc

07/12/2021, 8:09 AM

// `cache` is an interface that has method `newToken()` & `unrecoverableSession()`

Which one do you guys prefer, on the following snippet code? 1️⃣

if (retryCount > RETRY_LIMIT) {
             cache.unrecoverableSession()
             return null
        }

        cache.newToken()?.let { newToken ->
             return rewriteRequest(newToken)
        }

        return null

or 2️⃣

if (retryCount > RETRY_LIMIT) {
            cache.unrecoverableSession()
            return null
        }

        val newToken = cache.newToken()

        return if (newToken != null) {
            rewriteRequest(newToken)
        } else {
            cache.unrecoverableSession()
            null
        }

or 3️⃣

val newToken = cache.newToken()

        return when {
            retryCount > RETRY_LIMIT -> {
               cache.unrecoverableSession()
               null
            }
            newToken != null -> rewriteRequest(newToken)
            else -> {
               cache.unrecoverableSession()
               null
            }            
        }

3️⃣ 3

0️⃣ 1

07/15/2021, 9:17 AM

Hello, How to implement this below classes in better way? Class 1 has - DataResponse, Meta Response and List<IncludedResponse>

@Serializable
data class ApiResponse<T>(
    @SerialName("data") val data: DataResponse<T>,
    @SerialName("meta") val meta: MetaResponse?,
    @SerialName("included") val included: List<IncludedResponse>? = null
)

Class 2 has - List<DataResponse>, MetaResponse, List<IncludedResponse>

@Serializable
data class ListApiResponse<T>(
    @SerialName("data") val data: List<DataResponse<T>>,
    @SerialName("meta") val meta: MetaResponse?,
    @SerialName("included") val included: List<IncludedResponse>? = null
)

In both the class List<IncludedResponse>?
& MetaResponse
both are common only uncommon thing is

DataResponse

List<DataResponse>

miqbaldc

07/30/2021, 3:23 PM

Context: There’s a migration process from

UserV1

UserV2

from our shared prefs Which one do you prefer? 1️⃣

UserV1

UserV2

is nullable if fetched from server, but we provide a blank/default value

data class UserV1(status: String? = "", phoneNumber: String? = "", areaCode: Int? = -1)
data class UserV2(
   accountInfo: Account? = null,
   domicileInfo: Domicile? = null, 
)
data class Account(status: String? = "", phoneNumber: String? = "")
data class Domicile(areaCode: Int? = -1)

fun UserV1?.toUserV2() = UserV2(
    accountInfo = Account(status = this?.status.orEmpty(), phoneNumber = this?.phoneNumber.orEmpty()),
    domicileInfo = Domicile(areaCode = this?.areaCode ?: -1)
)
fun UserV2?.orEmpty() = UserV2()

// wrapping the whole if condition, e.g: (if a else b).orEmpty()
fun findUser() = (if (userV2?.status?.isNullOrBlank() == false) userV2 else userV1.toUserV2()).orEmpty()

2️⃣

UserV1

UserV2

is nullable if fetched from server, and leave it null (no blank/default value)

data class UserV1(status: String? = null, phoneNumber: String? = null, areaCode: Int? = null)
data class UserV2(
   accountInfo: Account? = null,
   domicileInfo: Domicile? = null, 
)
data class Account(status: String? = null, phoneNumber: String? = null)
data class Domicile(areaCode: Int? = null)

fun UserV1?.toUserV2() = UserV2(
    accountInfo = Account(status = this?.status.orEmpty(), phoneNumber = this?.phoneNumber.orEmpty()),
    domicileInfo = Domicile(areaCode = this?.areaCode ?: -1)
)
fun UserV2?.orEmpty() = UserV2()

// call the `.orEmpty()` twice, e.g: if a.orEmpty() else b.orEmpty()
fun findUser() = if (userV2?.status?.isNullOrBlank() == false) userV2.orEmpty() else userV1.toUserV2().orEmpty()

2️⃣ 1

Dennis Titze

08/12/2021, 11:51 AM

Hi all, I'm building a linter to learn & experiment, and I'm wondering if there are style or other guidelines you feel are relevant but not enforced by linters because it's more on the semantic than syntactic level? I read through this channel quite a bit already, but now I am wondering if there are topics similar to tabs vs. spaces where you have strong (and maybe different) opinions.

James Whitehead

08/12/2021, 1:56 PM

Hi all, I have a question regarding the methods

mutableSetOf()

and

linkedSetOf()

. Given that both methods return a

LinkedHashSet

is there a recommendation on when to use one vs the other?

Title

James Whitehead

08/12/2021, 1:56 PM

Hi all, I have a question regarding the methods

mutableSetOf()

and

linkedSetOf()

. Given that both methods return a

LinkedHashSet

is there a recommendation on when to use one vs the other?

diesieben07

08/12/2021, 2:09 PM

mutableSetOf

does not guarantee that you get a

LinkedHashSet

. All it guarantees is that you get a mutable set that preserves iteration order.

linkedHashSet

will always return a

LinkedHashSet

. So personally I'd always go for

mutableSetOf

unless you specifically need a

LinkedHashSet

➕ 2

👍 1

:thank-you: 1

View count: 3