CODEWITHSUNDEEP
scala
Therii
Therii

Reputation: 838

yielding values in for loop scala

I have 3 codes 1st is main code and remaining 2 codes uses for loop ,functionality of both codes is same .But both generate different o/p. Main code=>

class user(var name:String,var id:Int, var gender:Option[String])
{
override def toString="("+ name+","+id+","+gender+")"
}
object a
{
def main(args:Array[String]):Unit={
 var mm=Map(1-> new user("jh",189,Some("Male")),2->new      user("gh",12,None),3
->new user("io",100,Some("Female"))
 def getkey(i:Int)=
 { mm.get(i)
 }

Code 1 =>

var b=for{
h<-getkey(1)
i<-h.gender} yield i
print(i)
}
}

Code 2=>

var b=for{
h<-getkey(1)
i=h.gender} yield i
print(i)
} 
}

1st code has o/p some(Male) andd 2 nds o/p has Some(Some(Male)) Why both codes generate different o/p? If I replace <- with = in getkey(1) I get error .Why do we get it ?What is the use of <- in for ?

Upvotes: 1

Views: 55

Answers (1)

Leo C
Leo C

Reputation: 22439

Below is a slightly simplified version of your sample code:

class User(var name: String, var id:Int, var gender: Option[String])

val mm = Map(
  1 -> new User("jh", 189, Some("Male")),
  2 -> new User("gh", 12, None),
  3 -> new User("io", 100, Some("Female"))
)
def getkey(i:Int) = mm.get(i)

Code snippet 1:

for {
  h <- getkey(1)
  i <- h.gender
} yield i

can be translated to:

getkey(1).flatMap(_.gender)
// res1: Option[String] = Some(Male)

Code snippet 2:

for {
 h <- getkey(1)
 i = h.gender
} yield i

i = h.gender is an assignment and the for-yield is no different from:

for {
 h <- getkey(1)
} yield h.gender

and can be translated to:

getkey(1).map(_.gender)
// res2: Option[Option[String]] = Some(Some(Male))

Upvotes: 1

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