From: Simon Wright <simon@pushface.org>
Subject: Re: Problem with generic linked list package
Date: Sun, 10 Aug 2014 22:57:11 +0100
Date: 2014-08-10T22:57:11+01:00 [thread overview]
Message-ID: <lyr40oknyg.fsf@pushface.org> (raw)
In-Reply-To: 105213a0-7faa-48b1-a4ba-07791cd97c60@googlegroups.com
Laurent <daemon2@internet.lu> writes:
(actually I wrote this next section)
> type Rec is record
> B : Boolean;
> I : Integer;
> end record;
> function "<" (L, R : Rec) return Boolean is
> begin
> return L.I < R.I;
> end "<";
> Would that work for a record like this or would I have to define a
> function for every imaginable record?
>
> ie: type Rec is record
> S: String;
> I: Integer;
> D: Date;
> end record;
>
> Or could I do this (just a little piece of code hope you understand
> what I mean):
>
> els if Element.Rec.I < L.Head.all.Element.Rec.I then
> Add_To_Front (L, Element);
You have (after Shark8's suggestion, I think) a generic package which
starts something like
generic
type T is private;
with function "<" (L, R : T) return Boolean is <>;
package P is
...
If you want to instantiate it with a type Rec1
type Rec1 is record
B : Boolean;
I : Integer;
end record;
then you have somehow to provide a function to take the place of the "<"
in the generic formal part.
package P_For_Rec1 is new P (T => Rec1, "<" => ?something?);
where ?something? is a function which takes two parameters of type Rec1
and returns Boolean. It will be a Good Thing if ?something? returns True
if the first parameter is "less than" the second, *whatever "less than"
means in your application*.
If you want the comparison to be on the I component of Rec1, then you
could supply Less where
function Less (L, R : Rec1) return Boolean is (L.I < R.I);
(that's in Ada 2012), in which case you'd instantiate with
package P_For_Rec1 is new P (T => Rec1, "<" => Less);
The "is <>" in the formal part of package P means that you could
alternatively write
function "<" (L, R : Rec1) return Boolean is (L.I < R.I);
and
package P_For_Rec1 is new P (T => Rec1);
If you now decide you want to instantiate P with
type Rec2 is record
S: String;
I: Integer;
D: Date;
end record;
then you have to decide how
function Less (L, R : Rec2) return Boolean is (?);
needs to work. Do you need to compare the S component? the I component?
the D component? or some combination? But however it has to work, it has
to be a new function.
next prev parent reply other threads:[~2014-08-10 21:57 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-28 13:26 Problem with generic linked list package Laurent
2014-07-29 7:51 ` Jacob Sparre Andersen
2014-07-29 8:12 ` Laurent
2014-07-29 8:27 ` Stephen Leake
2014-07-29 15:38 ` Laurent
2014-08-07 19:07 ` Laurent
2014-08-07 19:21 ` Adam Beneschan
2014-08-07 19:25 ` Adam Beneschan
2014-08-07 22:20 ` Laurent
2014-08-07 23:35 ` Adam Beneschan
2014-08-08 4:42 ` Laurent
2014-08-09 14:32 ` Laurent
2014-08-09 14:58 ` AdaMagica
2014-08-09 15:22 ` Jeffrey Carter
2014-08-09 18:51 ` Shark8
2014-08-09 21:53 ` Laurent
2014-08-09 22:25 ` Jeffrey Carter
2014-08-10 8:22 ` Simon Wright
2014-08-10 10:45 ` Simon Wright
2014-08-10 20:20 ` Laurent
2014-08-10 21:57 ` Simon Wright [this message]
2014-08-10 23:42 ` Jeffrey Carter
2014-08-11 4:51 ` Laurent
2014-08-11 5:13 ` Jeffrey Carter
2014-08-11 7:56 ` Laurent
2014-08-07 20:37 ` Shark8
2014-08-07 22:30 ` Laurent
2014-08-07 23:22 ` Shark8
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