Indexing access for Lists and Maps considered harmful?

[Joshua Bloch]

I'm with Artur on this.  I think we're making a mountain out of a molehill.
 The fact that  collection.put(value) is an implementation detail.  The
value of (a = expr) is and should remain expr.
                   Josh

2009/6/24 <abies at adres.pl>

>
>
> "Reinier Zwitserloot" <reinier at zwitserloot.com> napisał(a):
>  > I am beginning to see some concensus on this list that the neal
>  > semantics are the most preferred semantics. That is:
>  >
>  > FOO = (a[b] = c);
>  >
>  > should be equal to:
>  >
>  > a[b] = c;
>  > FOO = a[b];
>  >
>  > and thus, both a setter and a getter call.
>
>
> I still don't understand why. It is not a case with current assignment
> operator.
> public class Test {
> volatile static int[] arr = new int[1];
> volatile static int val = 0;
> public static void main(String[] args) {
>    int x,y;
>    x = (val = 3);
>    y = (arr[0] = 5);
> }
> }
>
>
> compiles into
>
> public static void main(java.lang.String[]);
>  Code:
>   0:   iconst_3
>   1:   dup
>   2:   putstatic       #2; //Field val:I
>   5:   istore_1
>   6:   getstatic       #3; //Field arr:[I
>   9:   iconst_0
>   10:  iconst_5
>   11:  dup_x2
>   12:  iastore
>   13:  istore_2
>   14:  return
>
>
> Please note that there is no get from the arr nor from val, even if both
> are volatile and could be possible written into by another thread
> concurrently.
>
> x = (y = z)
>
> IS NOT EQUAL TO
>
> y = z;
> x = y;
>
> in current java.
>
> It is equal to
>
> tmp = z;
> y = tmp;
> x = tmp;
>
> I don't understand why suddenly for sugar-on-top-of-collections we have to
> change the rules which are valid for normal values and arrays. There is no
> 'getter' equivalent called for anything in java currently, if you will
> modify jvm to catch retrieve-value-from-array, it will not be invoked, so
> why should getter be called on collections?
>
> Regards,
> Artur Biesiadowski
>
>