Re: Why is this not legal

[Adam Beneschan <adam@irvine.com>]

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