Scala has a special syntax for invoking methods of arity-1 (one argument):
// is the same as
names mkString ","
This syntax is formally known as “infix notation”. It should only be used for purely-functional methods (methods with no side-effects) - such as mkString -or methods which take functions as parameters - such as foreach:
// right!
names foreach (n => println(n))
names mkString ","
optStr getOrElse ""
// wrong!
javaList add item
Read more: Scala documentation: Method Invocation
infix notation arity-1

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