Re: Reduction expressions

["Randy Brukardt" <randy@rrsoftware.com>]

"Simon Wright" <simon@pushface.org> wrote in message 
news:lyfrqynwpm.fsf@pushface.org...
> Lawrence D'Oliveiro <ldo@nz.invalid> writes:
>
>> On Tue, 20 Aug 2024 22:23:27 +0100, Simon Wright wrote:
>>
>>> "Randy Brukardt" <randy@rrsoftware.com> writes:
>>>
>>>> Accum_Subtype (we changed the name since it is a subtype, not a type;
>>>
>>> Amazing how a person (I) can have used Ada for ~40 years and still be
>>> hard put to it to describe the difference, at least in a case like
>>> this one, where the ARG members clearly see meanings that leave me
>>> lukewarm if not cold. Maybe "the heart of twilight"?
>>
>> I thought the difference was obvious. "subtype" is the C equivalent of
>> "typedef", just giving a new name to an existing type. So
>>
>>     subtype A is B;
>>
>> (where A and B are simple identifiers) is valid, whereas
>>
>>     type A is B;
>>
>> is not: a "type" declaration always creates a new type: you have to
>> write at least
>>
>>     type A is new B;
>>
>> and now you have two types with different names that are structurally
>> the same, but not compatible.
>
> Yes, I've understood that for a long time but ... ARM22 4.5.10(8,9)[1]
> say
>
> (8) The expected type for a reduction_attribute_reference shall be a
>    single nonlimited type.
>
> (9) In the remainder of this subclause, we will refer to nonlimited
>    subtypes Value_Type and Accum_Type of a
>    reduction_attribute_reference. ...
>
> and in AI 22-0011-1 [2] starting at 22-Oct-2021 5:25 PM,
>
> * SB: raises a series of observations,
> * STT: "... You really need to think of Accum_Type as a particular
>  *subtype*"
> * SB: "Ok, I was confused - Accum_Type is a subtype, not a type. So
>  a lot of my message was noise."
>
> If SB can be confused, so can I!

Which is why we changed the name - if SB can be confused, it is a good bet 
that there is something wrong with the wording. That's why I usually 
recommend bleeding edge users use the bleeding edge RM - no point in 
rediscovering all of the bugs that we already know about. Unfortunately, in 
this case, I'm the only one that has the bleeding edge RM because I haven't 
finished adding all of the approved AIs to it. This group is some that I've 
done, which is why the answer to your question was relatively easy to find.

                                 Randy.