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From: Rob Solomon <usenet@drrob1-noreply.com>
Newsgroups: comp.lang.ada
Subject: Re: Why is this not legal
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Date: Mon, 28 Sep 2009 22:06:47 -0400
Xref: g2news2.google.com comp.lang.ada:8527
Date: 2009-09-28T22:06:47-04:00
List-Id: <comp.lang.ada>

>On Sep 28, 5:11�pm, Rob Solomon <use...@drrob1-noreply.com> wrote:
>> I am trying to write some simple string manipulations but am getting
>> an error I don't understand.
>>
>> � type WordEntryType is String(1..MaxLineLength);
>>
>> This is flagged as not legal. �GNAT want it to read
>> IS NEW String
>>
>> But that means the type is not a standard string.
>>
>> What am I missing?
>
>The three letters "sub" in front of the keyword "type".
>
>TYPE declarations always create a new type.  SUBTYPE declarations will
>declare an identifier that refers to the same *type*, but puts
>additional constraints on it.  But if you use a SUBTYPE declaration,
>and you declare something of type
>
>  X : WordEntryType;
>
>then X's *type* will be STRING and you can pass it to procedures that
>require a STRING parameter.
>
>If this is still confusing to you, then I'd say you need to go back
>and read some more about Ada's type system.  This is an important
>feature of Ada that distinguishes it from C, Pascal, and possibly
>Modula (I don't know Modula well enough to say), and any decent
>introductory book on Ada should have a good exposition of this
>concept.
>
>                               -- Adam

That worked.  Thanks.

I find it confusing when I need a type vs subtype.  Modula-2 does not
have the subtype concept; it probably could use it though.

And your comment that a subtype adds constraints to a type also helps.

--rob