Scala: join an iterable of strings

How do I "join" an iterable of strings by another string in Scala?

val thestrings = Array("a","b","c")
val joined = ???
println(joined)

I want this code to output a,b,c (join the elements by ",").


How about mkString ?

theStrings.mkString(",")

A variant exists in which you can specify a prefix and suffix too.

See here for an implementation using foldLeft, which is much more verbose, but perhaps worth looking at for education's sake.