Re: Efficient Sequential Access to Arrays

["Vasiliy Molostov" <molostoff@gmail.com>]

Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> писал(а) в своём письме Fri,  
27 Jul 2012 10:28:45 +0400:

> 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.

no. We might object'read with any object. You are mixing abstraction  
layers here. Even you refer to "or other units".


>> 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?

You suppose sqlinterger as property of any db which is wrong.


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