From: Simon Wright <simon.j.wright@mac.com>
Subject: Generic instantiation with constrained subtype
Date: Sat, 23 Aug 2008 13:59:20 +0100
Date: 2008-08-23T13:59:20+01:00 [thread overview]
Message-ID: <m2bpzjopjr.fsf@mac.com> (raw)
I've been trying to write some test cases for the Booch Components and
came up with this.
The test case is written as a generic, to be instantiated with the
appropriate Container type. This is fine for the definite containers
(ie, ones like No_Problem below) but fails for the Bounded forms, which
use the Unconstrained/Constrained technique.
This is the example:
-----------------------------------------------------------------------
package Instantiation_Problem is
type Base is tagged null record;
type No_Problem is new Base with null record;
type Unconstrained (Constraint : Positive)
is new Base with null record;
subtype Constrained is Unconstrained (Constraint => 10);
generic
type T is new Base with private;
package G is end G;
package NP is new G (No_Problem);
package F is new G (Constrained);
-- ^--------------------18:24
package U is new G (Unconstrained);
-- ^--------------------21:24
end Instantiation_Problem;
-----------------------------------------------------------------------
and GNAT (GCC 4.3.0) says
instantiation_problem.ads:18:24: constraint on actual is incompatible with formal
instantiation_problem.ads:18:24: instantiation abandoned
instantiation_problem.ads:21:24: actual subtype must be constrained
instantiation_problem.ads:21:24: instantiation abandoned
Am I going to have to rethink this? Have I used the wrong way of
specifying the generic parameter? Is GNAT confused? (note, at 21:24 it's
asking for a subtype, so why complain at 18:24?).
Ideally I'd like it if any solution could work with Ada 95 - these are
the Booch Ada 95 Components!
--S
next reply other threads:[~2008-08-23 12:59 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-23 12:59 Simon Wright [this message]
2008-08-23 19:09 ` Generic instantiation with constrained subtype Jeffrey R. Carter
2008-08-23 20:24 ` Simon Wright
replies disabled
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox