Re: Ada-Singleton-Why does it work like this?

[Martin <martin.dowie@btopenworld.com>]

On 25 Mar, 11:17, Jean-Pierre Rosen <ro...@adalog.fr> wrote:
> I think there is a contradiction between "class" and "singleton". The
> term "class" is used, because it includes a set of objects that are
> equivalent for some point of view, i.e. a mathematical equivalence class.
>
> Now, if the class gathers only one object, the equivalence relationship
> does not make much sense...

It is a set - it just has a single member.

I think Singleton-as-a-type is useful if and only if you wish to
retain behavours you can acheive with other classes, e.g it may be
useful to mix in "stream-ability" or even polymorphism - e.g. you know
you can only have a single modem in your system but you may need to
have different modems (e.g. Hayes v. Alcatel. v. whoever).

Now in Ada we are used to doing that sort of thing via package renames
and compilation options. But perhaps that isn't an option in system
where modems can be replaced between power-down/power-ups.

Again, we used to seeing a different style of solving that problem in
Ada but that's not to say that solutions used in other languages
shouldn't be looked at on their own merits.

Perhaps the Patterns Working Group of the ACM could provide classic-
Ada-style v. GoF-style presentation? Or is it really that defunct?

Cheers
-- Martin