I am learning Scala and am a bit confounded by the difference between next types: 'Null', 'Nil' and 'Nothing'.
Can someone please help explain the difference to me? From what i gather, "Nil" is used to describe an empty list.
- 8Possible duplicate of Usages of Null / Nothing / Unit in Scalastopkillinggames.com– stopkillinggames.com2017-10-17 17:42:16 +00:00Commented Oct 17, 2017 at 17:42
- Please refer to scala api as you first point of reference: scala-lang.org/api/currentPavel– Pavel2017-10-17 17:44:57 +00:00Commented Oct 17, 2017 at 17:44
- @Alex L, thank you for the link. But I am still confused as to what Nothing is exactly used for. And I guess how does it differentiate with None which according to the API represents non-existent values?.... Also in the linked thread, the Curcyu pointed out that Nothing is used when the function does nothing at all... I don't really get the whole point of all the special subcategories of 'nothingness' and such.Linkx_lair– Linkx_lair2017-10-17 17:54:30 +00:00Commented Oct 17, 2017 at 17:54
- broadly, your question is a duplicate of stackoverflow.com/questions/16173477/…. if you have specific questions or doubts about specifics, consider opening one or more new questions about those specificsSeth Tisue– Seth Tisue2017-10-17 18:29:03 +00:00Commented Oct 17, 2017 at 18:29
- Just like Seth said - make your question more specific to what exactly you struggle to understand. Put your comment into a question.stopkillinggames.com– stopkillinggames.com2017-10-17 18:55:24 +00:00Commented Oct 17, 2017 at 18:55
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2 Answers
Nothingness in Scala
There are 7 cases where you want to represent the concept of nothingness in Scala.
Nil - Used for representing empty lists, or collections of zero length. For sets you can use Set.empty
None - One of two subclasses of the Optional type, the other being Some. Very well supported by the Scala collections.
Unit - Equivalent to Java's void which is used for functions that don't have a return type
Nothing - A trait. It is a subtype of all other types, but supertype of nothing. It is like the leaf of a tree. No instances of Nothing.
Null - A trait. Not recommended to be used.
null - An instance of the trait, similarly used as the Java Null. Not recommended to be used.
Best Practices
- If you have code that is returning null, change it to return an Optional.
- If you need to have an uninitialized variable, using Optional, or an empty list/collection instead of null *
For best practices recommendation, please see https://alvinalexander.com/scala/scala-null-values-option-uninitialized-variables
Why is null so hated?
- Please watch Tony Hoare's Billion Dollar Mistake
- Null pointer errors are hard to debug
Comments
In scala null is realy bad, you must use Optional[T].
We have Nil which is a empty list to be able to do 1 :: Nil to create a list that contain only 1.
And, Nothing is a subtype of every type. In other world, is a object that represent null.
3 Comments
Lee
Nothing doesn't 'represent' null, there are no values of type Nothing.
prayagupadhyay
There's no
Optional[T] in scala its Option[T]