Re: Inferring array index type from array object

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

On Wed, 23 Jun 2010 16:33:43 +0000 (UTC), Warren wrote:

> Niklas Holsti expounded in news:88ec2vF3uqU1@mid.individual.net:
>> Dmitry A. Kazakov wrote:
>>> On Wed, 23 Jun 2010 00:30:23 -0700 (PDT), Maciej Sobczak wrote:
> ..
>>>> 2. Is it possible to declare the index variable without hardcoding
>>>> the index type (that is, to infer it from the array object)?
>>> 
>>> No, without improving the type system. E.g. introducing abstract
>>> index types, and abstract range types (or more general sets of index
>>> types), and abstract composite types like arrays.
>> 
>> I don't think such large language changes would be necessary. The 
>> expression S'Range gives the compiler all the information about the
>> type and its constraints, so I see no reason why Ada could not be
>> extended simply to allow S'Range in a variable declaration, as in the
>> above quoted "I : S'Range". The declared variable "I" would have the
>> same (sub)type as the loop counter in "for I in S'Range loop ...".
> 
> I think most would agree that this is a "convenience" feature.
> I think the language (and its compiler) is probably complicated
> enough for these types of additions.

On the contrary, it is complicated because ranges and indices are irregular
types. Hard coded special cases make language more complex for both
programmer and compiler developer.

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