Re: Pascal ranges

["(see below)" <yaldnif.w@blueyonder.co.uk>]

On 31/12/2008 00:07, in article wcceizp1a3e.fsf@shell01.TheWorld.com,
"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote:

> "(see below)" <yaldnif.w@blueyonder.co.uk> writes:
> 
>> On 30/12/2008 23:19, in article wccmyed1cae.fsf@shell01.TheWorld.com,
>> "Robert A Duff" <bobduff@shell01.TheWorld.com> wrote:
>> 
>>>> .. The need for these closely
>>>> related subranges is rather smaller in Ada, e.g. thanks to array attributes
>>>> such as 'First and 'Last.
>>> 
>>> I don't understand why you say "need...rather smaller" here.
>>> I often have two subtypes of the same type, one for counting
>>> how many there are (0..N), and one for indexing into an array
>>> of them (1..N).  Like this:
>>> 
>>>     type Blah_Index is range 1..N;
>>>     subtype Blah_Count is Blah_Index'Base range 0..Blah_Index'Last;
>> 
>> Because we could write:
>> 
>>  type Blah_Count is range 0..N;
>> ...  array(Blah_Count range 1..Blah_Count'Last) of ...
> 
> Yes, we could write that, but more commonly, we might want to write:
> 
>  ...  array(Blah_Count range 1..Blah_Count'Last range <>) of ...
> 
> which is illegal, so we write:
> 
>  ...  array(Blah_Index range <>) of ...
> 
> Seems to me, in Ada, one often needs a name for both (the "count" and
> the "index").  And we need the index [sub]type anyway, so we can declare
> objects of it.  Such as the record component that records the last-used
> component of that array (which is inside the record).

Sure. I said the need was smaller, not non-existent. 8-)

My important point was that converting all Pascal subranges to distinct
types creates a need for pointless type conversions. These might do damage
to the type-safety mindset that is at least comparable with making
everything a subrange of Integer, as Pascal does.

-- 
Bill Findlay
<surname><forename> chez blueyonder.co.uk