Arrays are sufficient for ArrayLists? Really??

[Andrei Alexandrescu]

On 5/16/11 2:44 PM, Mehrdad wrote:
> On 5/16/2011 12:41 PM, Andrei Alexandrescu wrote:
>>> I was mistaken and removed my post. The code ingeniously redefines the
>>> problem - instead of removing from the array by shifting its tail
>>> downwards, it shifts elements upwards from the head of the array. A nice
>>> hack, but I don't think it does a lot in helping your situation.
>>
>> In fact I even need to take that back. In order to work correctly, the
>> function would have to iterate downwards. It _is_ indeed buggy, and I
>> should stop emitting opinions when I'm short on time...
>>
>> Andrei
>>
>
> I'm not sure what you mean by iterating downwards, but I just noticed
> another bug: That would _still_ stomp over a superarray if this array is
> a slice of it, right?

Iterating downwards would mean: if you want to remove the third element 
from

a = [0, 1, 2, 3, 4];

by using head shifting, you'd need to assign a[2]=a[1], a[1]=a[0] 
(backwards that is) to obtain [0, 0, 1, 3, 4]. Then you take a[1 .. $] 
which is the result.

The function as implemented first assigns a[1]=a[0] and then a[2]=a[1], 
leading to [0, 0, 0, 3, 4] which is not what's needed.

> Is there any way to find out if an array is a slice of another array?

No. If there would, it would be a rather advanced function. Allow me to 
reiterate my suggestion: it's likely you have a simple problem with a 
simple solution based on slices, which are a simple abstraction. 
Therefore I suggest you rethink a bit of your design, and it's possible 
you won't need assumeSafeAppend et al.


Andrei