Re: array from static predicate on enumerated type

[Thomas <fantome.forums.tDeContes@free.fr.invalid>]

In article <s2ofr1$1cg3$1@gioia.aioe.org>,
 "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:

> On 2021-03-15 18:48, Shark8 wrote:
> 
> > So, in Ada, there's no good choice for how to actually DO an array with 
> > gaps in the index:
> 
> That applies to all containers. The problem is mapping the key to a 
> dense position when the key is not dense or might be unordered.
> 
> There is no gaps in positions.
> 
> > But Array *isn't* a map, though often it is substituted as one.
> 
> Of course it is, per definition of mapping. f : key -> element.
> 
> > Array has further constraints, like the contiguous memory labeled above.
> 
> No. The constraint here is a dense index. That is not specific to a 
> general map or an array. It is a fundamental property of the set of keys 
> being a convex set. Convex ensures certain useful mathematical 
> properties invariant to the representation of the mapping. In 
> particular, it gives a way to enumerate elements.

> Arbitrary predicate kills convex, so the problem. Not array. A map would 
> have just same problem: a map of LETTERS is in general not substitutable 
> for a map of CURVED_LETTERS.


i don't understand,
since Ada.Containers.Ordered_Maps.Key_Type is private,
and so new Ada.Containers.Ordered_Maps (CURVED_LETTERS, Integer) is 
allowed.

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