Re: Pascal ranges

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"(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).

- Bob