Re: Reduction expressions

[Simon Wright <simon@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!

[1] http://www.ada-auth.org/standards/22rm/html/RM-4-5-10.html#p8
[2] http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ai22s/ai22-0011-1.txt?rev=1.2