Re: class wide iterable (and indexable)

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:q26lsh$1ee3$1@gioia.aioe.org...
> On 2019-01-22 00:15, Randy Brukardt wrote:
>> For instance, in a Vector, the
>> lower bound is fixed for all values of a particular type. That would
>> eliminate a lot of programming errors that happen in Ada programs (many
>> programs fail to deal with unusual lower bounds, because it's hard to get
>> right).
>
> I disagree. It would make array slices more difficult to use.

Array slices as defined in Ada aren't worth the substantial implementation 
complexity. I would replace them by slicing functions, and the bounds are 
lost.

> Presently we can do things like
>
>    Read (Buffer (From..To), Last);

Surely. But "Last" is a weird Ada-ism that exists solely because array 
bounds are so generally accessible. It is much more natural (and sensible 
for most uses) to return the count of characters read.

> Foo can move the index Last and this is the same index as outside in the 
> caller because indices do not slide. If you make the lower bound fixed, 
> indices would slide and that would require a lot of index arithmetic upon 
> calling subprograms on slices. This would be far more error-prone than 
> occasionally forgetting to use Buffer'First instead of 1.

True, in the rare case where that matters. But most of the time, one has to 
do that math to convert "Last" into a number of character read. So this is a 
wash to me - some things are easier, som things are harder. (Again, "Last" 
is an odd Ada-ism, specs would return a character count, not some array 
index.)

                              Randy.