Concatenate a List of Char into a String via a fold

Question

For a list of string, I do this:

val l = List("a", "r", "e")                    
l.reduceLeft((x, z) => x + z) 

I don't know how to do it for a list of Chars. The following is a compile error:

val chs = List('a', 'r', 'e')
chs.reduceLeft[String]( (x,y) => String.valueOf(x) + String.valueOf(y))

Answer 1

Here's the type signature for reduceLeft:

def reduceLeft[B >: A](f: (B, A) => B): B 

It requires that what you're reducing to be a subtype of the type that you're reducing from so in you're case Char is A and String is B which is not a subtype of Char.

You can do a foldLeft which will reduce your list and doesn't require the output to be a subtype of the input:

chs.foldLeft("")((x,y) => x + String.valueOf(y))