Is there any idiomatic way to avoid a huge when? L...

# announcements

[Pablo]

Is there any idiomatic way to avoid a huge when? Like
when(string){
"blabla" -> {generateA}
"bleble" -> {generateB}
"blibli" -> {generateC}
"bloblo" -> {generateE}
"blublu" -> {generateD}
....
}

Is there any pattern that could help me out with this? For instance Command or Factory? This when is going to grow when I add more items, note each item have different behavior

The example would be from my ViewModel I send this "type" to my useCase and my useCase decide what to do, because create N UseCase perhaps is a mess...

[nfrankel]

https://blog.frankel.ch/even-more-readable-code-without-if-else/

[Pablo]

Hmm, the thing is create a map to decide what to do then, right?

[nfrankel]

once you create a map, then you can get it out with the key e.g. "blabla", then call invoke() on the returned function

[jbnizet]

Another technique (maybe not applicable to your use-case, but maybe applicable too) is simply to use polymorphism or functions: instead of passing a string identifying what to do, pass what to do, as an instance of an interface or as a function. I.e. instead of something.execute('blabla'), use something.execute(BlablaCommand()) or something.execute { generateA() }

[Pablo]

@jbnizet yes that's something I saw, well I put String on this case, but can be whatever, I mean I can create an Enum/Interface and then use polymorphism for this. For example if I select youtube I want to do youtube://mydata/you.be if I want to do Twitter do twitter://tw.er/mydata something like this you know? Each type has a different behaviour but I can use whatever instead of sting so if you want to propose an example with your approach feel free.

[Rob Elliot]

enum class Scheme {
  youtube { override fun uriFor(data: String) = "youtube://$data/you.be" },
  twitter { override fun uriFor(data: String) = "<twitter://tw.er/$data>" };

  abstract fun uriFor(data: String): String
}

fun main(vararg args: String) {
  val schemeName = args[0]
  val data = args[1]
  Scheme.valueOf(schemeName).uriFor(data)
}

[Rob Elliot]

Or perhaps more flexible:

interface RemoteSystem {
  fun uriFor(data: String): String
}

class YouTube : RemoteSystem {
  override fun uriFor(data: String) = "youtube://$data/you.be"
}

class Twitter : RemoteSystem {
  override fun uriFor(data: String) = "<twitter://tw.er/$data>"
}

enum class Scheme {
  youtube { override val system = YouTube() },
  twitter { override val system = Twitter() };

  abstract val system: RemoteSystem
}

fun main(vararg args: String) {
  val schemeName = args[0]
  val data = args[1]
  Scheme.valueOf(schemeName).system.uriFor(data)
}

[Rob Elliot]

Except of course you’d use a proper way of constructing a URI…

import java.net.URI

enum class Scheme {
  youtube { override fun uriFor(data: String): URI = URI.create("youtube://$data/").resolve("<http://you.be|you.be>") },
  twitter { override fun uriFor(data: String): URI = URI.create("<twitter://tw.er/>").resolve(data) };

  abstract fun uriFor(data: String): URI
}

fun main(vararg args: String) {
  val schemeName = args[0]
  val data = args[1]
  Scheme.valueOf(schemeName).uriFor(data)
}

[Rob Elliot]

Though the more I think about it the more I like the map lookup Nicolas Fränkel suggested, because it makes it explicit that you’re doing a mapping from a string input to a domain object, and forces you to consider the possibility that there is no matching mapping:

interface RemoteSystem {
  fun uriFor(data: String): URI
}

class YouTube : RemoteSystem {
  override fun uriFor(data: String): URI = URI.create("youtube://$data/").resolve("<http://you.be|you.be>")
}

class Twitter : RemoteSystem {
  override fun uriFor(data: String): URI = URI.create("<twitter://tw.er/>").resolve(data)
}

val schemes = mapOf(
  "youtube" to YouTube(),
  "twitter" to Twitter(),
)

fun main(vararg args: String) {
  val schemeName = args[0]
  val data = args[1]
  val system = schemes[schemeName] ?: TODO("handle unknown scheme")
  system.uriFor(data)
}

[Rob Elliot]

Sorry, thinking about it I don’t really know why I barged into this 5 day old conversation without really thinking about and reading the preceding questions properly. Feel free to ignore.