[boost] Re: stride iterators and matricies

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-06-06 08:57:37

On 06/03/2005 02:47 PM, David Abrahams wrote:
> Neal Becker <ndbecker2_at_[hidden]> writes:
>>David Abrahams wrote:
[snip]
>>>B. What about the undefined behavior that results when you stride off
>>>   the end of a container?
>>
>>Is there any reasonable way to detect this?  If it is feasible without
>>significantly increasing cost, I'll add it - but offhand I don't know that
>>it is generally feasible.
>
> If it's random access you can store a base iterator and an index.
                                                              ^^^^^
Would "offset" be a better word?  An index, i, to me, implies
something satisfying:

    0 <= i < shape[axis]

where axis satisfies:

    0 <= axis < rank

where rank is the number of dimensions in the array and shape[axis] is
the length of the axis-th dimension.

With this defintion, I understand what you mean, i.e. instead of
the stride iterator incrementing the pointer, it would just store
the beginning of the object:

   X* px0;

and increment the offset.  Then dereferencing would simply:

   return *(px0+offset);

Is that you're meaning?