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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?= =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: Vocabulary matter: Component vs Element vs Item
Date: Thu, 25 Jul 2013 22:12:12 +0200
Organization: Ada @ Home
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Date: 2013-07-25T22:12:12+02:00
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Le Thu, 25 Jul 2013 21:01:38 +0200, Simon Wright <simon@pushface.org> a =
 =

=C3=A9crit:

> "Yannick Duch=C3=AAne (Hibou57)" <yannick_duchene@yahoo.fr> writes:
>
>> All three words "component", "element" and "item" could be seen as
>> interchangeable in plain English (or am I wrong?).
>
> I have a feeling that in English (BrE) "component" and "element" are
> more-or-less synonymous, but "item" isn't. "The solution to the proble=
m
> has five Xs" - X could be component or element, but not item; an item =
is
> a thing on its own, whereas a component or an element is one of many.

Sounds correct.

> So I think that the Ada Containers match this notion: a container can
> have elements (of element_type, eeew), and you replace one of them by =
an
> item.
>
> I see that the Booch Components have this the other way round:
>
>    procedure Insert (C : in out Abstract_Collection; Elem : Item)
>    is abstract;

After your note above, I now less feel it's an issue to mix both in a sa=
me  =

domain (or package, to speak Ada). Remains the case you point with the  =

swapped choice made in the Booch Components.

May be a way to solve it, is to have an Element_Type which is a subtype =
 =

(as a type aliasing) of Item_Type. This would allow to have both mixed  =

case while having consistency between an argument name and its type (the=
re  =

are cases where it's better to simply name a thing after its type).

Would look like this sample:


     type Instance_Type is =E2=80=A6;
     type Index_Type is =E2=80=A6;


     type Item_Type is =E2=80=A6;
     subtype Element_Type is Item_Type;

     -- Item_Type is defined first and
     -- Element_Type is a subtype of it,
     -- because Item_Type is defined
     -- independently of what will hold
     -- it. It exists as an item before
     -- it can become an element.


     procedure Append
       (Target : in out Instance_Type;
        Element : Element_Type);

     -- To the object receiving it,
     -- and which will hold it,
     -- it's an element.


     function Item
       (This : Instance_Type;
        I : Index_Type)
        return Item_Type;

     -- To the client receiving it,
     -- and which will hold it,
     -- it's first an item (may
     -- become an element later
     -- to it too).


Looks OK to me as I look at it. I believe I will opt for this convention=
.

Thanks for your not Simon. And Jeffrey too :-P (for the idea to look  =

somewhere else)


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D [1]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [1]
[1]: Epigrams on Programming =E2=80=94 Alan J. =E2=80=94 P. Yale Univers=
ity