Scala Call By Name Confusion

Question

I am working on some call by name examples using the REPL and running the same examples in Eclipse.

Here is what in Eclipse:
Scenario 1:

val fun         


        

Answer 1

There is no difference in the output. The difference is in what you want. From Eclipse you ran two things:

val funct = {println("Calling funct")} // prints Calling funct here
takesFunct(funct)

def takesFunct(f: => Unit)
{
   val b = f
}

and

val funct = {println("Calling funct")} // prints Calling funct here
takesFunct({println("Calling funct")}

def takesFunct(f: => Unit)
{
   val b = f                           // prints Calling funct here
}

On the REPL, the same thing happened according to your own logs:

scala> def takesFunct(f: => Unit)
{
  val b = f
}
takesFunct: (f: => Unit)Unit

scala> val funct = {println("Calling funct")}
Calling funct
funct: Unit = ()

scala> takesFunct(funct)
// No Output

Now, in the second scenario all you did was this:

scala> takesFunct({println("Calling funct")}
Calling funct

Since you did not repeat the val funct assignment, which was still present in Eclipse's second scenario, it did not print a message.

Note that

val funct = {println("Calling funct")}

is, as a practical matter, equivalent to

println("Calling funct")
val funct = ()