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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Dynamic type system for Ada
Date: Tue, 24 Jan 2017 15:21:41 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:33147
Date: 2017-01-24T15:21:41-06:00
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"Victor Porton" <porton@narod.ru> wrote in message 
news:o67mi7$v0f$1@gioia.aioe.org...
...
> All I ask is just an Ada type which would be so flexible that could store
> any kind of a value (just like as a variable in a dynamic language).
>
> This type could be a variant record which could store numbers, 
> lists/arrays,
> strings, etc. (anything that can be stored in a variable in a dynamic
> language).

I'd suggest that it be defined as an abstract tagged type, with each of the 
other kinds of things as a derived tagged type (one for holding integers, 
one for holding floats, etc.). Then one could get a "variable that could 
hold anything" by instantiating the Unbounded_Holder container (and that 
would open uses of the other kinds of containers as well). That way, the 
package wouldn't have to reinvent all of the memory management stuff that's 
already in the containers. Plus, if one organized the hierarchy similar to 
the chart in 3.2(12) 
[http://www.ada-auth.org/standards/2xrm/html/RM-3-2.html#p12], you could 
define shared operations at the appropriate levels to have some use beyond 
just plain storage. (For instance, all of the numeric types would have math 
this way.)

I do wonder how useful such a hierarchy would be, but I suppose someone 
would have to build it to find out.

                                   Randy.