How idiomatic is using an Immediately Invoked Function Expression (IIFE) with an Elvis after `let`, ...

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[Vishnu Haridas]

How idiomatic is using an Immediately Invoked Function Expression (IIFE) with an Elvis after let, also, apply etc. to execute some code when the receiver is null?

For example,

val response = getFromUrl(...)

response?.data?.user?.also {
    ...  // welcome the user, save data, and lot more.
} ?: {
    showError("Login failed")
} ()  // IIFE

[sindrenm]

Not my preference. It's unclear if it's invoked because response?.data?.user == null or because the also block returns null. It's also less readable than just an if statement, IMO. I'd do something like this, depending on what you want:

val user = response?.data?.user

if (user != null) {
   ...  // welcome the user, save data, and lot more.
} else {
  showError("Login failed")
}

[sindrenm]

Of course, in your example, if

...  // welcome the user, save data, and lot more.

returns null, then you'd also show the error, which is (probably?) not what you want?

[sindrenm]

Or … no, sorry, my bad. T.also returns T. Then I guess it's not really ambiguous, but still.

[Vishnu Haridas]

@sindrenm Got it! from your first answer, the ambiguity really depends upon the Scope function that we use. For example let & also - both has different outcomes.

[Perrankana]

I would use run instead of also in your case, this is how I understand it:`if response, data and user are not null then run a bunch of things`

[christophsturm]

why do you need the function at all, why not ?: showError(...)

[Vishnu Haridas]

@christophsturm true for a single line, but for a block of code, don't we need an IIFE?

[Burkhard]

One example is ?: run { log("null"); return }

[Adam Powell]

IIFE isn't a thing in kotlin, use run {} instead. run inlines, the IIFE does not, and will create a class/Function0.invoke call. Much less efficient.

[Adam Powell]

(you can verify this with the, "show kotlin bytecode" view in intellij/android studio)

[sindrenm]

I am a little curious as to who Stephan Schroeder is and what they have to do with this. 😮

[Vishnu Haridas]

@sindrenm actually I meant you only 😐 I hit enter as soon as I typed @ 🙈 and now only realized that I mentioned someone else 🤦🤦🤦 Updated now ✔️

[sindrenm]

Oh well, now they can get in on the fun, too! 🎉

Made me think of this

https://kotlinlang.slack.com/archives/CJLTWPH7S/p1572635193281700?thread_ts=1572624750.257500&cid=CJLTWPH7S