D array expansion and non-deterministic re-allocation

[Ali Cehreli]

Bartosz Milewski Wrote:

> > int[] a = [0];
> > auto b = a;
> > a ~= 1;
> > b ~= 2;
> > What is a[1]?
> >
> > Is this considered "stomping" and requiring a re-allocation?
> 
> Can this question be answered without the recourse to implementation, and the MRU cache in particular? 
> 
> I thought about an abstract definition of "stomping".Something like that: The expanded part of the array is never implicitly shared with any other array. But I'm not sure about this case:
> 

It is natural that a language like D has dynamic arrays (as core features or as library implentations). I think that's why we keep using the word "array" to describe slices. (No, I don't have proof for this theory.)

In *current* D, the user code does not handle dynamic arrays. Both 'a' and 'b' below are slices.

> int[] a = [1, 2, 3];
> int[] b = a[0..1];
> b ~= 4;
> what is a[1]?
> 
> By my definition, this would be considered stomping, but I couldn't find this example in TDPL. 

Neither 'a' nor 'b' own the elements; in that sense, if one is a slice then the other is a slice... In D, slices have "discretionary sharing semantics." Any slice may leave the sharing contract as it sees unfit.

Ali