Like the question says.
This was found in List[() => Unit] which was used to store callback functions.
I understand List[type] and that Unit is a return type of a function that doesnt return anything.
Add a comment |
2 Answers
(T1,...,Tn) => T is the type of functions that take parameters of types T1 through Tn and return type T. So () => Unit is the type of functions that take no parameters and have return type Unit. Consequently List[() => Unit] is the type of lists containing such functions.
2 Comments
Jesvin Jose
"parameters of types T1 through Tn", so functions like
f(T1):Unit, f(T2):Unit will be valid type for that list? What about something like f(T1,T2)?
sepp2k
@aitchnyu No. If you have a list of type
List[(T1, T2) => Unit] then that list stores functions that take two parameters (the first one having type T1 and the second T2) and return type Unit. So you could store a function defined as f(x:T1, y:T2):Unit in it, but not one defined as f(x:T1) or f(y:T2). Likewise a list of type List[() => Unit] only stores functions that take exactly no parameters.First off, you have a list of functions. Each function takes no parameters (this is what the open-close parentheses () mean) and returns Unit, which is a value for no result, similar to void.
In a pure functional world, a function of type ()=>Unit is useless because it takes nothing and returns nothing. However, Scala is not a purely functional language; it has side effects. To be useful, the functions in the list will surely have side-effects. Since they are callback functions, they also have an idea about when they fire.
