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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Community Input for the Maintenance and Revision of the Ada
 Programming Language
Date: Tue, 12 Sep 2017 19:41:39 +0200
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Date: 2017-09-12T19:41:39+02:00
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On 09/12/2017 08:18 AM, Tarjei Jensen wrote:
> 
> A counted string can be viewed as
> 
> type counted_string is record
>     max : natural;
>     len : natural;
>     str : array range ( 1 .. max) of character;
> end record;

This is, of course, illegal.

> The best known environment which uses counted strings is Turbo Pascal. Note that I wrote "uses". It is still being used in education.

In Ada 12, you can have something similar to Turbo Pascal's strings:

with Ada.Strings;

package B_Strings is
    type B_String (Max_Length : Positive := 1_000) is tagged limited private;
    -- This works in Ada 12 and only allocates Max_Length.
    -- Default initial value is Null_B_String

    Null_B_String : constant B_String; -- A string of zero characters

    function To_String (Source : B_String) return String;
    function "+" (Source : B_String) return String renames To_String;
    -- Lower bound of result is 1; upper bound is Length (Source)

    function To_B_String (Source : String) return B_String;
    function "+" (Source : String) return B_String renames To_B_String;
    -- Result's Max_Length will be Max (Source'Length, 1)

    function Length (Source : B_String) return Natural;

    Too_Long : exception;

    procedure Assign (To : in out B_String; From : in B_String; Drop : in 
Ada.Strings.Truncation := Ada.Strings.Error);
    -- Gives To the same value as From
    -- If Drop = Error and Length (From) > To.Max_Length, raises Too_Long
    -- To is unchanged if Too_Long is raised

    procedure Assign (To : in out B_String; From : in String; Drop : in 
Ada.Strings.Truncation := Ada.Strings.Error);
    -- Same as Assign (To => To, From => +From, Drop => Drop);

    function "="  (Left : B_String; Right : B_String) return Boolean;
    function "<"  (Left : B_String; Right : B_String) return Boolean;
    function "<=" (Left : B_String; Right : B_String) return Boolean;
    function ">"  (Left : B_String; Right : B_String) return Boolean;
    function ">=" (Left : B_String; Right : B_String) return Boolean;
private -- B_Strings
    type B_String (Max_Length : Positive := 1_000) is tagged limited record
       Len   : Natural := 0;
       Value : String (1 .. Max_Length) := (1 .. Max_Length => ' ');
    end record;

    Null_B_String : constant B_String := (Max_Length => 1, others => <>);
end B_Strings;

For earlier versions of Ada, you can eliminate the default for Max_Length, which 
may be even closer to what TP provides.

-- 
Jeff Carter
"Why don't you bore a hole in yourself and let the sap run out?"
Horse Feathers
49