CODEWITHSUNDEEP
scalafunctional-programming
Simon Huenecke
Simon Huenecke

Reputation: 97

Scala .map(toString()) gives List of Char

I tried to make my own map method in Scala and this is the result: 

def map[A, B](f: A => B)(as: List[A]): List[B] =
    for (i <- as) yield f(i)

And if I try to convert a List[Int] to a List[String]:

val list = List(1, 2, 3, 4, 5)   //> list  : List[Int] = List(1, 2, 3, 4, 5)
map(toString()) (list)           //> res0: List[Char] = List(e, b, u, n, g)

I get the same result if I try:

list.map(toString())             //> res1: List[Char] = List(e, b, u, n, g)

My Question: Why gives toString() not a List("1","2"...)?

Upvotes: 1

Views: 977

Answers (1)

sepp2k
sepp2k

Reputation: 370357

You're calling toString() on the current object (which apparently returns something like "?ebung...") and passing the resulting string as an argument to map.

So you might expect that to produce a type error because map expects a function, but you're passing a string. However strings count as functions too (because RichString implements the Function1[Int, Char] trait) that take an integer and return the character at that index. So that's why you get a list containing those characters.

To do what you meant to do (create a function that calls toString on its argument), you can either use x => x.toString or _.toString for short.

Upvotes: 4

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