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From: dennison@telepath.com (Ted Dennison)
Newsgroups: comp.lang.ada
Subject: Re: FAQ and string functions
Date: 2 Aug 2002 06:59:00 -0700
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bam@snoopy.apana.org.au (Brian May) wrote in message news:<29e5ffff.0208011621.3193755f@posting.google.com>...
> There is a replace function for the strings, I am a bit doubtful
> though if
> you can use it to expand the size of a fixed string...

To do that kind of thing, you will generally need to use slicing and
catenation ("&"). This is not really "expanding the size of a fixed
string", its creating a new (possibly fixed) string based on an old
one.

Recursion is often useful for this kind of thing. For instance
(warning: not compiled or tested):

function Transform (Source : String; From_Pattern : String; 
                    To_Pattern : String) return String is
   -- Find the location of the source pattern
   Pattern_Start : constant Natural := 
      Ada.Strings.Fixed.Index (Source => Source, Pattern =>
From_Pattern);
begin
   if Pattern_Start = 0 then
      return Source;
   else
      -- Return the string before the pattern, the new pattern, and a
      -- transformation of the string after the pattern.
      return Source (Source'First..Pattern_Start - 1) & To_Pattern &
         Transform (Source (Pattern_Start + From_Pattern'length ..
Source'last),
                    From_Pattern, To_Pattern
                   );
   end if;
end Transform;

> > I'm not a big fan of these kinds of renames. Why not instead just
> > write:
> > 
> > Put_Line (Class_Name (Package_ID, Get_Attribute (Value (I), "ref")) &
> >           "($1,$2,$3)");
> 
> Because if I need to use it multiple times, I think that means it will
> have to call get_attribute multiple times, won't it?

Quite true. I only said this because each was only used once in the
code you presented. If you needed multiple calls to Get_Attribute with
the same parameters (presumably returning the same result), then
assigning that result into a constant once would probably be better.

> Besides, I don't think the above makes it very clear what the
> significance
> is of the results of each function call.

Fair enough. But as someone reading your code the first time, I have
to say I found your transformation more confusing than the original.
Perhaps that's just me though...

> > If you insist in splitting it up, turn those renames into constants.
> Are constants better then renames? If so, why?


The problem with renames is that they can easily lead to aliasing. You
might end up having accesses, or worse, updates, or even *both*, to
both the original version and the aliased version. That kind of thing
makes it really difficult to follow data flow in your program. In the
case of renamed functions, it also obfuscates control flow.