Re: AbstractTraversable.headOption throws NoSuchElementException

A java.lang.Iterable should return a valid Iterator when requested. Any
implementation that doesn’t do that, is either faulty, or designed that way
thus not generally usable.
​

On Wed, May 6, 2015 at 2:25 PM, Rado Buranský <[email protected]>
wrote:

> The subject is not really correct, but I'd like to know you're opinion on
> how to avoid this kind of issue:
>
> import scala.collection.JavaConversions._
>
> val files: java.lang.Iterable[...] = ...
> files.headOption match { ... // This throws NoSuchElementException
>
> If you're curious the stack trace looked like this:
> ...
> Caused by: java.util.NoSuchElementException
> at
> com.google.common.collect.AbstractIterator.next(AbstractIterator.java:152)
> at
> scala.collection.convert.Wrappers$JIteratorWrapper.next(Wrappers.scala:42)
> at scala.collection.IterableLike$class.head(IterableLike.scala:91)
> at scala.collection.AbstractIterable.head(Iterable.scala:54)
> at
> scala.collection.TraversableLike$class.headOption(TraversableLike.scala:436)
> at scala.collection.AbstractTraversable.headOption(Traversable.scala:105)
> ...
>
> The reason is that the implementation of the Iterable can be iterated only
> once. But it took me a while to find it out. I simply called an API
> (SonarQube) to get a collection of files and I naturally didn't care about
> implementation of the Iterable interface. Should I? Who's fault is this and
> how to avoid it?
>
> Thanks for opinions
>
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