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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: for S'Image use Func??
Date: Thu, 06 May 2010 20:14:33 +0200
Organization: Ada At Home
Message-ID: <op.vcaqajn0ule2fv@garhos>
References: <Xns9D7085FECB88EWarrensBlatherings@188.40.43.213>
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Date: 2010-05-06T20:14:33+02:00
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Le Thu, 06 May 2010 19:10:20 +0200, Warren <ve3wwg@gmail.com> a =C3=A9cr=
it:

> I have tried to google for this and have not yet found
> a suitable answer, so I'll troll, er, poll for an
> answer here..
>
> Is there the ability to substitute your own S'Image
> function? For example, a basic interpreter might
> define:
>
>  type LNumber_Type is range 0..99_999;
>
> Can I declare..
>
>  for LNumber_Type'Image use LNumber_To_String;
>
> If so, then the question is what the signature of
> the S'Image function looks like-- is it:
As far as I could tell, your intuition is good, as there is indeed such =
 =

things in Ada, called either representation clauses or operational  =

clauses. See [ARM 2005 13.3] for more about it.

An excerpt to be kind:

[ARM 2005 13.3 (2)]
attribute_definition_clause ::=3D
       for local_name'attribute_designator use expression;
     | for local_name'attribute_designator use name;


[ARM 2005 13.3 (4)]
For an attribute_definition_clause that specifies an attribute that  =

denotes a subprogram, the expected profile for the name is the profile  =

required for the attribute.

However, it later says:

[ARM 2005 13.3 (5/1)]
An attribute_designator is allowed in an attribute_definition_clause onl=
y  =

if this International Standard explicitly allows it

Comes with a tiny example:


[AARM 2005 13.3 (6a)]
Ramification: This implies, for example, that if one writes:
for T'Read use R;
R has to be a procedure with two parameters with the appropriate subtype=
s  =

and modes as shown in

Finally, it should be checked if Image is explicitely allowed as an  =

attribute designator for an operational clause (I may check later to giv=
e  =

you a more formal answer to this one question).

I use representation clauses from time to time, but I've never used this=
  =

kind of one, for the reason I give you right after now.

>  function LNumber_To_String(LNO : LNumber_Type) return String;
>
> Finally, there is actually a third question- more along
> the lines of "Should this language feature be used
> in this manner?", or is it preferable to just code your
> own along the lines of (which is what I presently use):
>
>  function To_String(LNO : LNumber_Type) return String;
>
> Inquiring minds need to know,
>
> Warren
I would say, it is more handy to define a function, because a function  =

would be able to hold the exact formatting parameter your application  =

requires, it would be able to hold the exact optional defaults for those=
  =

parameters and it would better integrates with the overall general desig=
n  =

of an Ada application, that, =E2=80=9Cwithing=E2=80=9D package and using=
 renames clause.  =

Using attribute, you are require to always use thye type name as a prefi=
x  =

for such things as =E2=80=99Image. With function, you may =E2=80=9Cwithe=
d=E2=80=9D the package  =

defining this function, and make it part of the local scope using  =

something like =E2=80=9Cfunction F (...) ... renames My_Package.F ...=E2=
=80=9D.

More handy IMHO.

All of this providing I've understood what you were requesting for.

-- =

No-no, this isn't an oops ...or I hope (TM) - Don't blame me... I'm just=
  =

not lucky