What is the difference between def foo = {} and def foo() = {} in Scala?

by

If you include the parentheses in the definition you can optionally omit them when you call the method. If you omit them in the definition you can’t use them when you call the method.

scala> def foo() {}
foo: ()Unit

scala> def bar {}
bar: Unit

scala> foo

scala> bar()
<console>:12: error: Unit does not take parameters
       bar()
          ^

Additionally, you can do something similar with your higher order functions:

scala> def baz(f: () => Unit) {}
baz: (f: () => Unit)Unit

scala> def bat(f: => Unit) {}
bat: (f: => Unit)Unit

scala> baz(foo)    

scala> baz(bar)
<console>:13: error: type mismatch;
 found   : Unit
 required: () => Unit
       baz(bar)
           ^
scala> bat(foo)

scala> bat(bar)  // both ok

Here baz will only take foo() and not bar. What use this is, I don’t know. But it does show that the types are distinct.

More Related Contents:

  1. Using partial functions in Scala – how does it work?
  2. What is Scala’s yield?
  3. What is the difference between Scala’s case class and class?
  4. What is the motivation for Scala assignment evaluating to Unit rather than the value assigned?
  5. Difference between reduce and foldLeft/fold in functional programming (particularly Scala and Scala APIs)?
  6. Abort early in a fold
  7. What are some compelling use cases for dependent method types?
  8. Scala currying vs partially applied functions
  9. val-mutable versus var-immutable in Scala
  10. Increase JVM heap size for Scala?
  11. Using Either to process failures in Scala code
  12. When to use parenthesis in Scala infix notation
  13. When and why should one use Applicative Functors in Scala
  14. Function returns an empty List in Spark
  15. Functional programming, Scala map and fold left [closed]
  16. How to pattern match into an uppercase variable?
  17. What is a function literal in Scala?
  18. How to sort a list in Scala by two fields?
  19. Can I zip more than two lists together in Scala?
  20. Cross product in Scala
  21. Functional Reactive Programming in Scala [closed]
  22. Multiple parameter closure argument type not inferred
  23. Difference between using App trait and main method in scala
  24. Any reason why scala does not explicitly support dependent types?
  25. Scala: write string to file in one statement
  26. Why is appending to a list bad?
  27. Calculate Cosine Similarity Spark Dataframe
  28. Why does Scala support shadow variables? [closed]
  29. How to wait for several Futures?
  30. Spark ML VectorAssembler returns strange output

Leave a Comment