difference between def/val assignment

[Christoph Driessen]

Hi all,

running the following code yields

null
null
null
new value

class Data {
     var value: String = _
}

object DataTest {
     def main(args: Array[String]) {
         def a = new Data
         val b = new Data

         println(a.value)
         println(b.value)

         a.value = "new value"
         b.value = "new value"

         println(a.value)
         println(b.value)
     }
}

Can anyone explain the difference between def and val in this  
situation? Playing around with both I cannot find any difference  
between 'a' and 'b', they are both the same class. But 'a' must be  
something different. What exactly is it then?

Cheers,
Christoph

[Kevin Wright-4]

because of the "def", a is a function that returns a new Data every time it's called
the Java equivalent of

    def a = new Data

would be

    Data a() { return new Data(); }


So each of the following statements refers to a unique instance of Data:

println(a.value)
a.value = "new value"
println(a.value)

On Wed, Jul 8, 2009 at 12:35 PM, Christoph Drießen <ced@...> wrote:

Hi all,

running the following code yields

null
null
null
new value

class Data {
   var value: String = _
}

object DataTest {
   def main(args: Array[String]) {
       def a = new Data
       val b = new Data

       println(a.value)
       println(b.value)

       a.value = "new value"
       b.value = "new value"

       println(a.value)
       println(b.value)
   }
}

Can anyone explain the difference between def and val in this situation? Playing around with both I cannot find any difference between 'a' and 'b', they are both the same class. But 'a' must be something different. What exactly is it then?

Cheers,
Christoph

[Chris Twiner]

hiya,

def declares a method, each subsequent access makes the expression run
again. In this line:

        a.value = "new value"

you get a new Data, set its value and discard it.  The only "trick" is
that, as in this case, you can define one without parameters, but it
will always re-evaluate.

I hope the rest makes sense given that.

cheers,
Chris

On Wed, Jul 8, 2009 at 1:35 PM, Christoph Drießen<ced@...> wrote:

> Hi all,
>
> running the following code yields
>
> null
> null
> null
> new value
>
> class Data {
>    var value: String = _
> }
>
> object DataTest {
>    def main(args: Array[String]) {
>        def a = new Data
>        val b = new Data
>
>        println(a.value)
>        println(b.value)
>
>        a.value = "new value"
>        b.value = "new value"
>
>        println(a.value)
>        println(b.value)
>    }
> }
>
> Can anyone explain the difference between def and val in this situation?
> Playing around with both I cannot find any difference between 'a' and 'b',
> they are both the same class. But 'a' must be something different. What
> exactly is it then?
>
> Cheers,
> Christoph
>