Why is this not legal

Why is this not legal

[Rob Solomon]

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?

Thanks

Re: Why is this not legal

[Adam Beneschan]

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

Re: Why is this not legal

[Rob Solomon]

>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

Re: Why is this not legal

[stefan-lucks]

While the question has been answered, and the wikibook is a good 
reference, this appears to be a frequently asked question. Obviously, 
GNAT's error message in this case ("missing new") is leading beginners
into the wrong direction. 

Stefan

On Wed, 30 Sep 2009, Martin Krischik wrote:

> Rob Solomon schrieb:
> > 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 question has been answered but for more info see:
> 
> http://en.wikibooks.org/wiki/Ada_Programming/Type_System
> 
> ;-)
> 
> Martin
> 

-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------

Re: Why is this not legal

[Martin Krischik]

Rob Solomon schrieb:
> 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 question has been answered but for more info see:

http://en.wikibooks.org/wiki/Ada_Programming/Type_System

;-)

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

Re: Why is this not legal

[Keith Thompson]

Adam Beneschan <adam@irvine.com> writes:
[...]
> 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.
[...]

Small correction: a subtype declaration may or may not add additional
constraints.  For example:

subtype My_String is String;

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"