scala pattern matching on functions

Question

I am looking for a way to do pattern matching based on the result of a function evaluation rather than the type of the val. For example,

def f1(x:String):Boolean = if (x contains ("Helllo")) true else false
val caller="Hello"

caller match 
{
  case f1(caller) => println ("caller said hello")
  case _ => println ("caller did not say hello")
}

any idea ?

It sounds like you basically want the equivalent of Haskell's ViewPatterns extension. — user824425
– user824425, Commented Sep 7, 2013 at 16:06
I get what u mean, but if it is only strings then u cna probably use regex for pattern matching. — Jatin
– Jatin, Commented Sep 7, 2013 at 16:29

wingedsubmariner · Accepted Answer · 2013-09-07 16:30:55Z

2

You want to use pattern guards:

caller match 
{
  case x if f1(x) => println ("caller said hello")
  case _ => println ("caller did not say hello")
}

answered Sep 7, 2013 at 16:30

wingedsubmariner

13.7k1 gold badge32 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

CruncherBigData Over a year ago

thank you so much @wingedsubmariner did not even know that pattern guards existed. Thanks again.

4lex1v · Accepted Answer · 2013-09-08 11:27:39Z

0

I would prefer to do it without guard, that would a bit faster and cleaner:

f1(caller) match {
  case true => ....
  case false => ....
}

but for Boolean better to use if/else expression, that would be cleaner in byte code and a bit faster

answered Sep 8, 2013 at 11:27

4lex1v

21.6k7 gold badges56 silver badges88 bronze badges

1 Comment

fbiville Over a year ago

The advantage of guards afaik is they need not be applied to all cases at once.

Collectives™ on Stack Overflow

scala pattern matching on functions

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related