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From: kst@sd.aonix.com (Keith Thompson)
Subject: Re: Design of Ada.Strings.Bounded
Date: 1997/07/13
Message-ID: <EDA684.Dnr@thomsoft.com>#1/1
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Organization: Aonix, San Diego, CA, USA
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Date: 1997-07-13T00:00:00+00:00
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In <5q4mel$16r$1@goanna.cs.rmit.edu.au> Dale Stanbrough <dale@goanna.cs.rmit.EDU.AU> writes:
> After contemplating how i would use Ada.Strings.Bounded, i wondered about
> the decisions that were made when it was designed. 
> 
> If I use it in a package, and want to add any additional features, or
> use it as a parameter type
> 
> e.g. 
> 	function Check_Spelling (Item : Bounded_80) return Boolean;
> 
> then this is rather unfortunate when i want to check the spelling 
> of an item in a Bounded_81 string.

Probably the easiest way to handle this is to declare Check_Spelling
to take a parameter of type String.  To pass it a parameter of type
Bounded_80, just call To_String.

I do wonder, though, why the maximum length of a Bounded_String was
made a generic parameter rather than a discriminant.  Thus, rather than

   ...
   package Ada.Strings.Bounded is
   ...
      generic
	 Max : Positive;
      package Generic_Bounded_Length is
	 type Bounded_String is private;
	 ...
      end Generic_Bounded_Length;
   end Ada.Strings.Bounded;

we could have

   ...
   package Ada.Strings.Bounded is
      ...
      type Bounded_String(Max_Length : Positive) is private;
      ...
   end Ada.Strings.Bounded;

This would slightly complicate the function To_Bounded_String (it would
need an extra parameter to specify the Max_Length of the result),
but it would otherwise simplify the use of Bounded_Strings from
the user's point of view.  It would also allow operations between
Bounded_Strings of different Max_Lengths.  On the other hand, it
might make operations on Bounded_Strings slightly less efficient,
since they'd have to allow for the discriminant values.

Was this approach considered?  If so, why was it rejected?

-- 
Keith Thompson (The_Other_Keith) kst@sd.aonix.com <http://www.aonix.com> <*>
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