Re: Ada Basics

["David C. Hoos" <david.c.hoos.sr@ada95.com>]

Where is the procedure Increment declared?

----- Original Message -----
From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada.eu.org>
Sent: Wednesday, October 09, 2002 1:37 PM
Subject: Re: Ada Basics


>
> "prashna" <vashwath@rediffmail.com> wrote in message
> news:d40d7104.0210090453.f6aed66@posting.google.com...
> > Hi all,
> > What is the difference between declaring a type by using new (ex type
> > one_to_hundred is new Integer range 1..100) and declaring a type
> > without using new (type one_to_hundred is range 1..100)?
>
> As has been pointed out, the new form indicates derivation, which means
the
> primitive operations of the parent type are inherited by the derived type.
>
> For type Integer, it's not obvious what's happening, but consider another
> type:
>
> package P is
>    type T is range 0 .. 200;
>    procedure Inc (O : in out T);
> end;
>
> Here, we have an integer type, that has (in addition to the pre-defined
> operations for integer types) an increment operation, allowing you to do
> this:
>
> X : T := 0;
> Increment (X);
>
> Now let's create another type that derives from T:
>
> with P;
> package Q is
>    type NT is new P.T;  --range is 0 .. 200
> end;
>
> Type NT inherits the operations of its parent type T, which means NT has
an
> increment operation:
>
> Y : NT := 0;
> Increment (Y);
>
> In this example, T is the root of a family of types, and all types in this
> family have an Inc operation.  This is useful if you want to pass any
member
> of this family as a generic formal type:
>
> with P;
> generic
>    type NT is new P.T;
> package GR is ...;
>
> In this example, you can instantiate GR with either P.T or Q.NT:
>
> with P;
> package R is new GR (P.T);
>
> with Q;
> package R is new GR (Q.NT);
>
> In the body of GR, you can apply the Inc operation to objects of formal
type
> NT.
>
> For scalar types, you're allowed to constrain the range of the parent.  In
> the example above, NT has the same range as its parent (0 .. 200), but we
> could have made it smaller if that were desired:
>
> with P;
> package Q is
>    type NT is new T range 1 .. 100;  --constrain range
> end;
>
> In general, a derivation is allowing you to state that there is a
> relationship between the types.  If no such relationship is necessary,
then
> just declare the type without a derivation:
>
> package Q is
>    type T is range 0 .. 200;
> end;
>
>
>
>
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada
>