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Newsgroups: comp.lang.ada
Date: Tue, 5 Jan 2016 20:54:44 -0800 (PST)
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Subject: Re: Instantiating package problems
From: Anh Vo <anhvofrcaus@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:29025
Date: 2016-01-05T20:54:44-08:00
List-Id: <comp.lang.ada>

On Tuesday, January 5, 2016 at 8:52:00 PM UTC-8, Anh Vo wrote:
> On Tuesday, January 5, 2016 at 7:31:00 PM UTC-8, Andrew Shvets wrote:
> > On Monday, January 4, 2016 at 3:49:32 PM UTC-5, Anh Vo wrote:
> > > On Sunday, January 3, 2016 at 4:07:30 PM UTC-8, Andrew Shvets wrote:
> > > > Hi Bob,
> > > >=20
> > > > Thanks for writing back.  This is the entire example:
> > > > http://pastebin.com/GEJT3WzL
> > > =20
> > > Just recommend to add a precondition to function Division as shown be=
low. By the way, this feature is part of latest Ada (Ada 2012). In addition=
, you should think about adding precondition to other operations such as Ad=
dition where Input1 + Input2 <=3D Integer'Last and Input1 + Input2 >=3D Int=
eger'Last.=20
> > >=20
> > >   function Division(
> > >     Input1 : in Integer;
> > >     Input2 : in Integer)
> > >       return Integer
> > >    with pre =3D> Input2 /=3D 0;
> > >=20
> > > Anh Vo
> >=20
> > I'm not sure that that worked.  I added it to my ads file and after com=
pilation and then re-running the application, this is what I got:
> >=20
> > ....
> >=20
> >  Division:        4
> >=20
> >=20
> > raised CONSTRAINT_ERROR : calculator.adb:33 divide by zero
> >=20
> > Shouldn't the division function been prevented from running the actual =
division operation beforehand?
>=20
> The preconditions and postconditions are controlled by pragma Assertion_P=
olicy. Thus, pragma Assertion_Policy(Check) must be added at the top of the=
 package specification. Absent of this pragma is equivalent to pragma Asser=
tion_Policy (Ignore). That means these conditions are ignored. By the way, =
ASSERTION_ERROR exception would be raised instead of CONSTRAINT_ERROR.

The call would be rejected off hand with ASSERTION_ERROR raised at the poin=
t of the call.