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From: G. B. <nonlegitur@nmhp.invalid>
Newsgroups: comp.lang.ada
Subject: Re: class wide iterable (and indexable)
Date: Tue, 8 Jan 2019 18:32:58 -0000 (UTC)
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Date: 2019-01-08T18:32:58+00:00
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Randy Brukardt <randy@rrsoftware.com> wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:q0pvlp$1vp1$1@gioia.aioe.org...

> That's primarily the job of package specifications, how the contents are 
> structured isn't very relevant from a description standpoint.
> 
> ...
>>> ...
>>>> No, interfaces cannot contain common code except for class-wide one. Is
>>>> that what Randy meant about overhead?
>>> 
>>> Not really. My main point is that you'll never have more than one 
>>> concrete
>>> instance of a generic interface in any individual program (certainly not 
>>> of
>>> an interface like that of a container),
>> 
>> I don't understand this. Usually I have dozens of instantiations of the 
>> same generics with different actual parameters.
> 
> Right, but all of those are *different* interfaces because they have 
> *different* generic parameters. You can't mix those types in any useful way, 
> because you almost always have the generic parameter type(s) involved.
> 
> For instance, for the containers, an interface would have to contain the 
> element type. But that substantially limits reuse, because almost every 
> container instance would have a different element type. You can't even pass 
> just the interface into a generic because you wouldn't be able to call the 
> primitives without knowing the element type. To make such a reuse possible 
> you'd have to pass so many parameters that you are typing instantiations for 
> days. And then the compilation time also would be days. You'd have to be 
> slightly mad to even try it. :-)

For software design, then, does it seem reasonable to assume that the
result of a generic instantiation is not for reuse, but for use? So that,
therefore, if an algorithm can handle different instances of a generic,
this algorithm would specify them through a generic formal?

(Inversion of structure.)