How does Scala's groupBy identity work?

Question

I was browsing around and found a question about grouping a String by it\'s characters, such as this:

The input:

\"aaabbbccccdd\"
         


        

Answer 1

Whenever you try to use methods such as groupBy on the String. It's important to note that it is implicitly converted to StringOps and not List[Char].

StringOps

The signature of groupBy is given by-

def groupBy[K](f: (Char) ⇒ K): Map[K, String]

Hence, the result is in the form -

Map[Char,String]

List[Char]

The signature of groupBy is given by-

def groupBy[K](f: (Char) ⇒ K): Map[K, List[Char]]

If it had been implicitly converted to List[Char] the result would be of the form -

Map[Char,List[Char]]

Now this should implicitly answer your curious question, as how scala figured out to groupBy on Char (see the signature) and yet give you Map[Char, String].