CODEWITHSUNDEEP
scalacollectionsscala-option
user3103957
user3103957

Reputation: 848

find method in scala's collection

Per the documentation, find function in scala's collection wraps the resulting elements in Option object. In the below, the size operation ends in error; where as the endsWith produces correct result.

The second element in the list being null, both should error out / produce correct result.

val a1:String = "ABCDEF"
val a2:String = null
val res12 = List(ABCDEF, null)

res12 filter { _.size > 10 }              //errors out
java.lang.NullPointerException
  at scala.collection.immutable.StringOps$.length$extension(StringOps.scala:51)
  at scala.collection.immutable.StringOps.length(StringOps.scala:51)
  at scala.collection.SeqLike.size(SeqLike.scala:108)
  at scala.collection.SeqLike.size$(SeqLike.scala:108)
  at scala.collection.immutable.StringOps.size(StringOps.scala:33)
  at .$anonfun$res19$1(<console>:13)
  at .$anonfun$res19$1$adapted(<console>:13)
  at scala.collection.TraversableLike.$anonfun$filterImpl$1(TraversableLike.scala:251)
  at scala.collection.immutable.List.foreach(List.scala:392)
  at scala.collection.TraversableLike.filterImpl(TraversableLike.scala:250)
  at scala.collection.TraversableLike.filterImpl$(TraversableLike.scala:248)
  at scala.collection.AbstractTraversable.filterImpl(Traversable.scala:108)
  at scala.collection.TraversableLike.filter(TraversableLike.scala:262)
  at scala.collection.TraversableLike.filter$(TraversableLike.scala:262)
  at scala.collection.AbstractTraversable.filter(Traversable.scala:108)
  ... 28 elided

res12 find { _.endsWith("EF") }       //produces correct result
res20: Option[String] = Some(ABCDEF)

Upvotes: 0

Views: 1055

Answers (2)

jwvh
jwvh

Reputation: 51271

both should error out / produce correct result

No they shouldn't.

filter() has to touch every element to see if it's in or out. If there's a bomb in the collection then it will be detonated.

find() is lazy. Find the 1st element to pass the predicate test and we're outa here. One and done.

Upvotes: 3

Brian
Brian

Reputation: 20285

This produces an error because you are calling size on a null String which is in fact a NullPointerException

scala> val s: String = null
val s: String = null

scala> s.size
java.lang.NullPointerException
  at scala.collection.StringOps$.size$extension(StringOps.scala:165)
  ... 32 elided

Upvotes: 1

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