Re: basic question on adding 2 arrays

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 07/13/2014 03:10 AM, AdaMagica wrote:
> On Sunday, July 13, 2014 8:33:57 AM UTC+2, Jeffrey Carter wrote:
>> function "+" (Left : in Base_Grid; Right : in Base_Grid) return Base_Grid with
>> Pre => Left'Length = Right'Length;
>>
>> Next (Next'First + 1 .. Next'Last - 1) :=
>>      Next (Next'First .. Next'Last - 2) +
>>      Next (Next'First + 2 .. Next'Last);
>
> OK, one can do this, but is it better than Nasser's?
>
>>     for i in 2..next'length-1 loop
>>        next(i):= now(i-1)+now(i+1);
>>     end loop;

That's a different question, and depends on the definition of "better".

Using 'Length rather than 'Last is probably not a good idea for defining an 
index into an array.

If the problem domain has lots of these partial-array operations, then defining 
and using such operators might be more readable. If not, explicit loops might be 
better. If these arrays are very large and space or time are tight, one might 
need to concern oneself with low-level questions such as whether using an array 
operator results in a temporary result and extra copy.

-- 
Jeff Carter
"I would never want to belong to any club that
would have someone like me for a member."
Annie Hall
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