From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,2078dddcdcd8d83
X-Google-Attributes: gid103376,public
From: "John G. Volan" <johnvolan@sprintmail.com>
Subject: Re: Warning: Religious naming convention discussion :-) [was: assign
 help!!]
Date: 1997/05/16
Message-ID: <337CF962.40DC@sprintmail.com>#1/1
X-Deja-AN: 242068052
References: <5kjvcv$evt@news.cis.nctu.edu.tw> <5kn8ko$jcc@top.mitre.org>
 <1997May7.201035.2439@nosc.mil> <33727EEA.2092@sprintmail.com>
 <5kuf1j$17vi@uni.library.ucla.edu> <3373666A.31DFF4F5@spam.innocon.com>
 <5li43j$ur3@castor.cca.rockwell.com>
Reply-To: johnvolan@sprintmail.com
Newsgroups: comp.lang.ada
Date: 1997-05-16T00:00:00+00:00
List-Id: <comp.lang.ada>


Wayne Magor wrote:
> 
>      Altitude : Units.Feet;
>      Latitude : Units.Radians;
>      Rate     : Units.Hertz;
> 
> It's pretty important to know that Altitude is in feet and not nautical miles
> or meters.  It's also pretty important to know what is in Degrees and what
> is in Radians.  This is the most straightforward and elegant solution, IMHO.

I'll say it again: If something is important enough to say in the type,
then it's just as important to say it in the object names, too:

   Altitude_Feet    : Units.Feet;
   Altitude_Meters  : Units.Meters;

   Latitude_Radians : Units.Radians;
   Latitude_Degrees : Units.Degrees;

   Rate_Hertz       : Units.Hertz;
   Rate_Megahertz   : Units.Megahertz;

If you're using many different units for the same kinds of quantity, all
in the same program, then it's important to keep them all straight.

But this pattern is basically just Booch style:

   <specific_modifier>_<general_noun> : <general_noun>;

(For example "Altitude" can be seen as the specific modifier attached to
the general noun "Feet".)

Now, if you can guarantee me that you'll always be attaching some
modifier or other, then this approach is workable.  (Just don't ask me
to try this sort of thing on my object-oriented abstractions... "The_"
is just noise.)

On the other hand, if your project intends to settle on _one_ standard
universal unit for each type of quantity (a good idea anyway), then
embedding the unit name in the objects, or the types, or both, is just
noise (i.e., Hungarianism).  Better to just say, a la Booch:

   The_Altitude : Altitude;
   The_Latitude : Latitude;
   The_Rate     : Rate;

or, a la Cohen: 

   Altitude : Altitude_Type;
   Latitude : Latitude_Type;
   Rate     : Rate_Type;

Sure, it'll take discipline to always keep to the project-standard
units. But (short of wrapping these up as private types) keeping to the
units would take discipline _anyway_. Just because the type name says
"Feet" doesn't guarantee programmers will always remember to treat them
as feet... but if you think the programmers need reminding, better
remind them with every object!

------------------------------------------------------------------------
Internet.Usenet.Put_Signature 
  (Name => "John G. Volan",  Home_Email => "johnvolan@sprintmail.com",
   Slogan => "Ada95: The World's *FIRST* International-Standard OOPL",
   Disclaimer => "These opinions were never defined, so using them " & 
     "would be erroneous...or is that just nondeterministic now? :-) ");
------------------------------------------------------------------------