The great slice debate -- should slices be separated from arrays?

[Andrei Alexandrescu]

Steven Schveighoffer wrote:
> In many other posts, people have been festering over dropping T[new] and 
> not having a reference array type.  The argument is (and forgive me if 
> this is a strawman, someone from the other side can post if I'm 
> incorrect): If we make arrays a separate type from slices, and only 
> allow appending on arrays, then we solve the stomping problem and the 
> hard-to-determine reallocating problem.  For those who are unfamiliar 
> with these problems, I'll try to outline them at the bottom of the post.
> 
> I contend that even if we make arrays a separate type, even if arrays 
> are made a true reference type, slices will still suffer from the same 
> hard-to-determine reallocation problem *unless* we make slices fatter.
> 
> My proof is as simple as an example.  Assume 'Array' is the new type for 
> an array:
> 
> auto a = new Array!(int)(15); // allocate an array of 15 integers, all 0
> auto s = a[0..5];
> a ~= [1,2,3,4,5];
> a[0] = 1.
> 
> Now, what does s[0] equal?

Array may include a field

    bool sliceExtracted;

that is set to true whenever you take a slice from the array and set to 
false whenever the array's data is reallocated. The array's 
documentation could mention that ~= is amortized constant if there are 
no intervening slicing operations.


Andrei