Re: Efficient Sequential Access to Arrays

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 26 Jul 2012 22:25:58 -0700 (PDT), Shark8 wrote:

> On Thursday, July 26, 2012 12:56:49 PM UTC-6, Dmitry A. Kazakov wrote:
>> On Thu, 26 Jul 2012 10:40:32 -0700 (PDT), Shark8 wrote:
>> 
>>> On Thursday, July 26, 2012 7:46:04 AM UTC-6, Dmitry A. Kazakov wrote:
>>>>
>>>> Some would disagree, but IMO in a well-written Ada program you should never
>>>> ever need 'Valid. Don't do Unchecked_Conversion with doubtful outcome.
>>>> Don't use stream attributes for constrained types.
>>> 
>>> It might not be avoidable though; the presence of 'Valid however does let
>>> you ensure that your [sub]typing assumptions are met.
>> 
>> These assumptions must be upheld per value construction.
> 
> Er, yes? Your value-construction procedure, which might be a
> stream-implementation, could use 'Input to ensure the data is valid, no?
> Then isn't the 'Read the value-construction?

Neither. If you use stream you should do it properly, i.e. as the transport
layer. The transport is defined in terms of bytes, characters or other
units. So the only read here might be Character'Read.

> Many DBs don't support such range subtyping, so why is it "bad form" to
> ensure that such values, when read (ie value construction from the
> database) conform to the proper subtypes. (Though this might be done
> automatically on assignment from function if it falls outside the
> 'Range... I'll have to read up on when subtype constraints are applied.)

When DB client does not support type mapping, you should always use the DB
native type, e.g. SQLINTEGER. Ada type must be obtained from that using
type conversion.

Which should be obvious if we remember that Ada discourages implicit type
conversions. Why a DB to Ada one should be implicit?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de