On Saturday, 9 April 2016 at 19:25:32 UTC, Uranuz wrote:
Another observation is illustrated with the foloving code: http://dpaste.dzfl.pl/8d68fd5922b7Because AA and arrays are not created before they were assigned some value it leads to inconsistency in behavior. And will produce unexpected and hidden bugs that is not good. It's not very good side of D's array and AA. But classes could be also affected by this *feature* (or bug, as you wish). So we must always construct reference semantics types before passing them to functions that will modify it. For classes it's obvious but for AA and dynamic arrays is not.
The inconsistency is only there with associative arrays, where adding a key may or may not affect other views of the AA, depending on if the AA was empty before or not.
In code: ---- int[int] aa1; ... int[int] aa2 = aa1; aa2[0] = 0; /* may or may not affect aa1 */ ----With dynamic arrays, appending does never affect other views, no matter if the array was empty or not.
In code: ---- int[] a1; ... int[] a2 = a1; a2 ~= 1; /* never affects a1 */ ----Dynamic arrays do have a similar oddity, but it doesn't depend on empty/non-empty. It depends on the capacity. When you append to a dynamic array that has no capacity left, a new copy of the data is made. The dynamic array then becomes independent of other ones with which it used to share data.
In code: ---- int[] a1 = [0]; ... int[] a2 = a1; a2 ~= 1; /* never affects a1 */ a2[0] = 1; /* may or may not affect a1 */ ----With class references I can't see any inconsistency. When you're given a null reference, all you can do is construct an object there, which never affects other copies of the reference. And when you mutate through a non-null reference, that always affects other copies of the references, of course.
In code:
----
class C {int x = 0;}
C c1;
...
C c2 = c1;
c2 = new C; /* never affects c1 */
c1 = c2;
c2.x = 1; /* obviously affects c1 */
----
Another solution is to pass reference types by *ref*. So you will not have such bugs in implementation
Yup, if you mean to affect the passed variable, ref is the way to go. And if you don't mean to affect the passed variable, you should probably mark the parameters const, or at least the reference part of the parameters (e.g. const(int)[]).
