Hi. I have the following code ```val version = service.getAllTemplates() .find { ... } ?.version...

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[Vitali Plagov]

Hi. I have the following code

val version = service.getAllTemplates()
  .find { ... }
  ?.versions // returns a list
  ?.single()
  ?: error("no template found matching the given predicate")

I’m using the find{} on purpose so I could handle its failure with a proper error message,
I want to do the same with single(). I want to throw an exception with my own error message if the list contains more than one element.
I tried singleOrNull() but still can’t provide a separate error message for it. Looks like the last error(…) handles both nulls.

[mkrussel]

You could add an extension method that calls singleOrNull() and handles the error.

Or possibly add the first error after find with some parentheses.

[Vitali Plagov]

Or possibly add the first error after find with some parentheses.

What do you mean by that? Can’t understand how to make it 🤔

[Alex]

You could try getOrElse()

[mkrussel]

val version = (service.getAllTemplates().find { ... } ?: error("no template found matching that given predicate")
  .versions // returns a list
  .singleOrNull()
  ?: error("no template found matching the given predicate")

But I would probably go with

val template = service.getAllTemplates().find { } ?: error("no template found matching that given predicate")
val version = template
  .versions // returns a list
  .singleOrNull()
  ?: error("no template found matching the given predicate")

Something like that, I haven't tested it. getOrElse is probably also a useful solution.

[mkrussel]

But in general putting the error by where the error happens is easier to understand.

[ephemient]

IMO the clearest thing to do would be to split out the separate error cases, e.g.

val template = service.getAllTemplates().find { ... }
    ?: error("no template ...")
val version = template.versions.singleOrNull()
    ?: error("...")

[Vitali Plagov]

Thank you all! I think splitting is a good option. I will go with it