Functions without arguments, with unit as argument in scala

Question

def foo(x: Int, f: Unit => Int) = println(f())

foo(2, { Unit => 3 + 4 })

// case 1
def loop: Int = 7
foo(2, loop) // does not compile

changing loop to 
// c         


        

Answer 1

()=>Int is Function0[Int] while Unit=>Int is Function1[Unit,Int]

scala> val function0: () => Int = () => 5
function0: () => Int = 

scala> val function1: Unit => Int = u => 5
function1: (Unit) => Int = 

scala> function0()
res0: Int = 5

scala> function1("anything")
res1: Int = 5

scala> function1(100)
res2: Int = 5

scala>

Also note that () is an object of Unit

scala> function1(())
res11: Int = 5

scala> function1 ()
res12: Int = 5

scala> function1()
res13: Int = 5

scala> val unit = ()
unit: Unit = ()


scala> function1(unit)
res15: Int = 5

scala> function1 apply unit
res16: Int = 5

scala>