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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Reduction expressions
Date: Tue, 20 Aug 2024 23:30:54 -0000 (UTC)
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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.