https://kotlinlang.org logo
Join SlackCommunities
Powered by
# effective-kotlin
  • a
    It's very weak
  • a
    Looking at recursing because I forgot about parsing internal functions šŸ˜ž
  • a
    and there's probably way more I missed
  • a
    To be fair, 
    when
    statements did totally save my life but without being able to use sealed classes I've been forced to "poke and prod"
  • a
    can you point to a line where you found the casting frustrating?
  • a
    Okay, here's one example: this is one I desperately wish to refactor because the code is so ugly
  • a
    property_getting.kt
    property_getting.kt
  • a
    Oh, I may have insight since I first wrote this over 6 months ago (before I even saw your talk on sealed classes) on some potential refactoring tips and refactored a little but but not much. However, I feel like if I didn't have this string check, I'd have to wrap whens - is there a way to check if a Node has a child type but it is not an immediate child, or do we just keep on pattern matching down
  • a
    Not sure If I am 100% clear on what you mean by "has a child type" (is the child a field on the Node? Or do you mean some other class somewhere is a child of Node?)
  • a
    either way there may be a trick with 
    when
    and Ranges that can help you
  • a
    on the left side of the branch you can evaluate if something is 
    in
    a Range, but you can overload the 
    contains()
    operator
    to make it check just about anything...
  • a
    Copy code
    operator fun Regex.contains(text: CharSequence): Boolean = this.containsMatchIn(text)

class Substring(private val str: String) {
  operator fun contains(text: CharSequence): Boolean = text.contains(str)
}
  • a
    then you can write something like:
    Copy code
    when ("hello") {
    in Regex("h*llo") -> println("Regex")
    in Substring("ello") -> println("Substring")
}
    šŸ˜® 1
  • a
    This is really just syntactic sugar though as you can put anything on the left that returns a Boolean
  • l
    The 
    Substring
    class could be inline BTW
    šŸ‘ 2
  • t
    as per my post in #general Iā€™m keen join/start conversations about how to leverage what Kotlin provides to write code thatā€™s clear at the site of use - because we spend most of our time reading code, not writing it. this helps others (and a lot of the time, ā€œothersā€ means ā€œfuture me whoā€™s forgotten why he wrote this in the pastā€ šŸ˜‰) https://kotlinlang.slack.com/archives/C0922A726/p1558405181100800
    • 1
    • 1
  • f
    Something I've noticed about Kotlin is it does a good job of enforcing its ideals on you (in a good way)
  • f
    Like final by default classes, and smart casts from immutabillty
  • f
    I guess one tip for effective kotlin would be to avoid mutable values and 
    lateinit
  • f
    I've heard people saying that you should never have nullable variables in kotlin, and "It's just a remnant from Java". What do you think about that?
    t
    d
    r
    • 4
    • 4
  • f
    I've been seeing all these libraries using type-safe builders in a way that seems insane It basically goes like this (as a simplified example): Instead of having
    Copy code
    class User(val name: String,val email:String)
    They do
    Copy code
    class User{
var name : String 
var email: String
}
fun user(init: User.() -> Unit) = User.apply{init()}
    What are the benefits of this?
    t
    • 2
    • 3
  • f
    I would love to get anyone to comment on this discussion (on slack) https://github.com/mipt-npm/plotly.kt/issues/12
  • k
    Hi. I need to open a BottomSheetFragment on button click. What is the better approach 1- Should i create a global instance and create it once
    Copy code
    val dialog by lazy { Dialog() }
    2- Should i create it inside method each time button is clicked
    Copy code
    btn.setOnClickListener { showDialog() }

fun showDialog() {
    Dialog().show()
}
    f
    • 2
    • 1
  • k
    Hello, is there a way to tell the compiler to place my data classes as inner classes to an object/interface type so that I can define my data classes in different files, but still have them as inner classes to use as namespacing?
  • g
    Does lateinit has a performance cost? I mean it adds additional if check for every access to the variable?
    f
    • 2
    • 1
  • k
    Greetings, is it possible to create an extension function on a specific Enum value?
    šŸš« 1
    x
    • 2
    • 1
  • s
    Here why the "is there" string not get concatenated?
  • d
    because your + statement is part of else ...
  • d
    or rather will only execute in else case..
  • d
    test it by changing the value of a = "C" and see if it prints C is there