resizeable arrays: T[new]

[Bruno Medeiros]

Walter Bright wrote:
> Sean Kelly wrote:
>> Walter Bright wrote:
>>> (The problem is if I pass a slice to a function, and then that 
>>> function reallocates the slice by changing the length or appending to 
>>> it, it can affect other slices into the same data in very 
>>> hard-to-explain ways.
>>
>> I'm not sure I understand how a reallocation could affect other slices 
>> into the same data.  If a reallocation occurs, that reallocation will 
>> be into entirely new memory, provided the slice doesn't start at the 
>> head of a memory block.  Is it the condition I just mentioned that's a 
>> problem?  If so, I suppose it is one way to trick the compiler into 
>> thinking the reference no longer refers to const data, when in fact it 
>> does.  If not, could you point me in the right direction?
> 
> Given:
> 
>     int[] a = new int[7];
>     int[] b = a[1..6];
>     b[1] = 2;   // writes through to a[2]
>     b.length = 4;
>     b[1] = 3;   // writes through to a[2]
>     b.length = 6;
>     b[1] = 4;   // does not write through to a[2]
> 

So, is that the problem we are trying to solve? Why not just simply make 
it so that setting .length *allways* creates a new array?

Hum, now that I think about it, this may not only be a better solution, 
it may be the *only* real solution. Even, with the new 
resizable/unresizable array proposal you can have the same problem as above:

   int[new] a = new int[7];
   int[new] b = a;
   b.length = 6;

   b[1] = 2;   // writes through to a[1]
   b.length = 4;
   b[1] = 3;   // writes through to a[1]
   b.length = 10;
   b[1] = 4;   // does not write through to a[1]

Why does this problem exist? Because, setting an array length may or may 
not create a new array, and there isn't a way to know which will happen. 
  Well, in that code segment we can see when it will resize, but we 
can't know in the general case (like when we receive an array as a 
function parameter). This makes setting .length as very unsafe 
operation, if not plain *broken*.

(Oskar, I would particularly like to hear your opinion on this)

-- 
Bruno Medeiros - MSc in CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D