I love how `when` cleans up my code. Used with `in...

# announcements

[hallvard]

I love how when cleans up my code. Used with in, checking if an element is in a collection is very simple. Now have I overlooked the possibility of doing it the other way around? I.e. is it possible to do something like this (pseudo-code):

when (collection-of-strings) {
  has "string 1" -> handleString1()
  has "string 2" -> handleString2()
  has "string 3" -> handleString3()
  else -> throw Exception()
}

[fred.deschenes]

You can do something like this :

with(collection-of-strings) {
        when {
            contains("string 1") -> handleString1()
            contains("string 2") -> handleString2()
            contains("string 3") -> handleString3()
            else -> throw Exception()
        }
    }

not as clean though

[orangy]

One problem is that in when first match wins, and semantics here is not clear. Should it “handle” every element in a collection, or just first match?

[orangy]

Also lookup for each check is not optimal, obviously, especially when collection has O(n) contains

[hallvard]

@fred.deschenes It may not be as consise as my wish-for example, but it still is a huge win vis-à-vis of the endless if {} else if ... that we did in java ...! Thanks for pointing it out!

[fred.deschenes]

@hallvard np, but keep in mind what @orangy mentioned above

[hallvard]

@orangy Good points, thanks.

[orangy]

There is also a proposal to generate better switch with invokedynamic for Java: http://mail.openjdk.java.net/pipermail/amber-spec-observers/2018-April/000568.html
This can be done manually in your case by using something like

when(listOfStrings.indexOfWhich("a", "b", "c")) {
 0-> // a
 1-> //b
}

[orangy]

indexOfWhich can be implemented efficiently, but there is no such function in stdlib currently