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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Strings with discriminated records
Date: Sun, 27 May 2018 10:39:33 +0200
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Date: 2018-05-27T10:39:33+02:00
List-Id: <comp.lang.ada>

On 2018-05-27 03:42, NiGHTS wrote:
> On Saturday, May 26, 2018 at 7:42:22 PM UTC-4, Shark8 wrote:
>> You can do this:
>>
>> Type Message(Length : Positive) is record
>>    Text  :  String(1..Length);
>>    -- Other components.
>> end record;
> 
> More interesting to me would be to pass a string literal as a discriminant. Using your example, something like this...
> 
> Type Message (Length : Positive; Text_Value : String) is record
>    Text  :  String(1..Length) := Text_Value;
>    -- Other components.
> end record;
> 
> This gives me an error: Discriminants must must have a discrete or access type

There is no constructors and no user-defined aggregates, which you are 
actually asking for, but sometimes a constructing function does the job:

    function Create (Value : String) return Message is
    begin
       return (Length => Value'Length, Text => Value);
    end Create;

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