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From: Mats.Weber@matrix.ch (Mats Weber)
Subject: Re: Ada.strings.bounded problems?
Message-ID: <Mats.Weber-1301952029290001@mlma11.matrix.ch>
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References: <TARJEIJ.95Jan11183331@ulrik.uio.no> <D29L78.J9@nntpa.cb.att.com>
 <3f3rl7$kts@watnews1.watson.ibm.com>
Date: Fri, 13 Jan 1995 19:29:29 GMT
Date: 1995-01-13T19:29:29+00:00
List-Id: <comp.lang.ada>

In article <3f3rl7$kts@watnews1.watson.ibm.com>, ncohen@watson.ibm.com wrote:

> There IS a way to implement bounded strings with the bound given as a
> constraint, so simple that it is found in many introductory examples: 
> 
>    package Bounded_Strings is
>       type Bounded_String (Max_Length: Positive) is private;
>       ...  -- all sorts of useful operations
>    private
>       type Bounded_String (Max_Length: Positive) is
>         record
>            Current_Length : Natural := 0;
>            Text           : String (1 .. Max_Length);
>         end record;
>    end Bounded_Strings;
> 
> This approach is easily generalized to other kinds of arrays.

The BIG problem with this approach is that testing two Bounded_Strings for
equality is erroneous (Ada 83 terminology). In Ada 95, this would be a
bounded error, but two bounded strings may compare different while being
logically equal. The problem comes from the unused characters in Text
beyond Max_Length.

Mats