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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: array from static predicate on enumerated type
Date: Fri, 12 Mar 2021 23:16:29 +0100
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On 3/12/21 9:49 PM, Matt Borchers wrote:
> Say, for example, I define a static predicate on a sub-type of an enumerated type, like:
> 
> type LETTERS is ( A, B, C, D, E, F, G, H, I , J, K );
> 
> subtype CURVED is LETTERS
>      with Static_Predicate CURVED in B | C | D | G | J;
> 
> What I want is an array over CURVED (using CURVED as the index), but since attributes 'First and 'Last (and thus 'Range) is not allowed, this cannot be done.
> 
> Has anybody come up with a clever data structure to make sub-types with predicates easy and sensible for indexing (not iterating)?
> 
> I only need read access ...
It sounds as if you want a map, for which one of the map containers in the 
standard library would be appropriate.

-- 
Jeff Carter
"[I]t is foolish to polish a program beyond the
point of diminishing returns, but most programmers
do too little revision; they are satisfied too
early."
Elements of Programming Style
189