Automatic Eta Expansion
The conversion of methods into functions has been improved and happens automatically for methods with one or more parameters.
def m(x: Boolean, y: String)(z: Int): List[Int]
val f1 = m
val f2 = m(true, "abc")
This creates two function values:
f1: (Boolean, String) => Int => List[Int]
f2: Int => List[Int]
The syntax m _ is no longer needed and will be deprecated in the future.
Automatic eta-expansion and nullary methods
Automatic eta expansion does not apply to "nullary" methods that take an empty parameter list.
def next(): T
Given a simple reference to next does not auto-convert to a function.
One has to write explicitly () => next() to achieve that
Once again since the _ is going to be deprecated it's better to write it this way
rather than next _.
The reason for excluding nullary methods from automatic eta expansion
is that Scala implicitly inserts the () argument, which would
conflict with eta expansion. Automatic () insertion is
limited in Dotty, but the fundamental ambiguity
remains.