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kotlinlang

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.

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

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

&gt; Or possibly add the first `error` after `find` with some parentheses.
What do you mean by that? Can’t understand how to make it :thinking_face:

```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.

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

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("...")```

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