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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Naming convention to identify functions with side effects
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Date: Mon, 29 Sep 2008 21:52:18 +0200
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Date: 2008-09-29T21:52:22+02:00
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On Mon, 29 Sep 2008 11:55:49 -0700 (PDT), Adam Beneschan wrote:

> It's this last that is connected to one of my pet peeves.  Say you've
> decided to write a routine to load a particular web page, and you've
> made it a Boolean function that returns True if it's successful:
> 
>    function Load_Web_Page (URL : String) return Boolean;
> 
> Several times, I've heard people say (in similar cases) that the name
> should be something like this:
> 
>    function Web_Page_Is_Loaded (URL : String) return Boolean;
> 
> so that it's grammatically correct when you put it in an IF statement:
> 
>    if Web_Page_Is_Loaded ("http://www.irvine.com") then...
> 
> This is WRONG, WRONG, WRONG!!!  It may make your IF statement look
> more grammatically correct, but it OBSCURES what the program is
> doing.  The above "grammatically correct" statement looks more like a
> check to see if the page is already loaded; a programmer reading this
> will not be able to figure out that the function call is the routine
> that actually does the loading.  This is much better:
> 
>    if Load_Web_Page ("http://www.irvine.com") then...

I don't like either. They hide the side-effect instead of publishing it.
Is_Loaded is a property of a page, it is not of an URL. To me it should be:

   type Web_Page is ...;
   function Load (URL : String) return Web_Page;
   function Is_Loaded (Page : Web_Page) return Boolean;

Should pages be cached, then the cache of pages must be exposed:

   type Web_Page is ...;
   type Web_Pages_Cache is ...;
   procedure Load (Cache : in out Pages_Cache; URL : String);
   function Is_Loaded (Cache : Pages_Cache; URL : String) return Boolean;
   function Get_Loaded (Cache : Pages_Cache; URL : String)
      return Web_Page;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de