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From: anon@att.net
Newsgroups: comp.lang.ada
Subject: Re: Why constant components are not permitted ?
Date: Sat, 26 Nov 2011 00:23:28 +0000 (UTC)
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Date: 2011-11-26T00:23:28+00:00
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--
--  To use constant with "record" define record then create an object 
--  with preset value that contains the key word "constant"
--

procedure a is

  type test_type is record
                 a : integer ;
                 b : string ( 1 .. 4 ) := "this" ; -- default
                 c : string ( 1 .. 10 ) ;
               end record ;


  -- tst is a constant record with all values are unchangable
  
  tst : constant test_type := test_type ' ( 16#FFFF# , 
                                            "that", 
                                            "0123456789" ) ; 

begin
  null ;
end ;



In <9ja2aiFla6U1@mid.individual.net>, Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>On 11-11-25 11:06 , AdaMagica wrote:
>> Useful applications for constant components could be (this is what you
>> can have in C++):
>>
>> record  -- *not* Ada
>>    Name: constant String   := "James Bond";
>>    Id  : constant Positive := 007;  -- e.g employee number of a company
>>    other variable components
>> end record;
>
>The original poster specified the constant value in the declaration of 
>the record *type*, not separately for each record *object*. This is what 
>I do not understand: what is the use of a value that is the same for all 
>objects in which it can appear?
>
>The "type constants" that Ada now provides are the attributes of a type 
>(tag, size, and so on), as Ludovic pointed out.
>
>I understand that some would like to have a "write once" kind of record 
>component that can be given a value once, when a record object is 
>created, and cannot be changed afterwards. Discriminants are like that 
>in Ada, but cannot be of arbitrary type.
>
>-- 
>Niklas Holsti
>Tidorum Ltd
>niklas holsti tidorum fi
>       .      @       .