scala - Confused about function literals -

scala newbie here.

i have set defined , declared follows:

var g = set(1,2,3) 

now want print out each element of set follows using function literal:

scala> g.foreach(s => println(s)) 1 2 3 

all good.

i can more concise this:

scala> g.foreach(println) 1 2 3 

all good.

now when this:

scala> g.foreach(println()) <console>:9: error: type mismatch;  found   : unit  required: int => ?               g.foreach(println()) 

why fail? me (a newbie), seems equivalent of g.foreach(println). please can explain error.

when pass function literal or function directly, in first 2 examples, do not invoke function immediately. however, in last example do invoke it, because println() syntax calling functions , methods. because println() result type unit, you're in fact passing value of type unit method expects value of type (string) => unit, , of course these different values, compiler shows error.