Hi folks, I’m playing with elvis(?:) operator and ...

# getting-started

[blue]

Hi folks, I’m playing with elvis(?:) operator and looking for some help, I want to return from the method when my object is null but before returning from the method I want to add a log statements, what is the correct way of doing that?

val record = (repository.findById(id) ?: (<http://log.info|log.info>("log message here") return))

[Paul Griffith]

IMO if you have more than a single statement you should just use a regular if statement. That said, you can use run for this;

val record = repository.findById(id) ?: run { 
	<http://log.info|log.info>("log message here") 
	return 
}

[Richard Gomez]

I agree with Paul: readable code is better than clever code.

[ephemient]

to be clear:

val record = repository.findById(id)
if (id == null) {
    <http://log.info|log.info>("log message here")
    return
}

will work equivalently, as the val is smart-cast to non-null after the conditional

[ephemient]

although if <http://log.info|log.info> returns Unit you can get away with

val record = repository.findById("id") ?: return <http://log.info|log.info>("log message here")

but I do not recommend it; stylistically, I would tend to avoid treating Unit as a value where unnecessary

[Michael Böiers]

This seems to be one of these situations where the “old-fashioned” ways of doing things work best. Just like in Java you don’t always use Optional, in Kotlin you shouldn’t always use the elvis operator and/or scope functions. Simple > clever.

[Klitos Kyriacou]

Do the "clever" examples of syntax above actually compile? They don't for me. The compiler says that a value of type Record is required where I instead return Unit.

[Stephan Schroeder]

you never gave us the return type of the function you're in, so people assumed it's Unit 😉
Assuming your method returns Record (which is what your error message seems to tell us), this leads to the question: So what do you want to return in case repository.findById(..) returns null?
I see three possibilities:
• return a nullable Record
• throw an exception

val record = repository.findById(id) ?: run { 
	<http://log.info|log.info>("log message here") 
	throw NoSuchElementException("no record found with id $id") 
}

• return a default

val defaultRecord = ... //should be outside of the method, so you always return the same instance
...
val record = repository.findById(id) ?: run { 
	<http://log.info|log.info>("log message here") 
	return defaultRecord
}

of course you can only return a default value if a logical/useful default value exists. otherwise return null. null in Kotlin is more benevolent than in Java, since it can't surprise you, so use it where appropriate.

[Michael Böiers]

May be beside the point, but the logging you want to do is a little excessive. If not finding the record could be a problem, maybe it would be better to throw an exception and do the logging elsewhere. Another good solution could be to change the signature of the method so that it requires a record to start with. Methods with a lot of guard clauses that do “silent” returns can be difficult to maintain.