From: Maciej Sobczak <no.spam@no.spam.com>
Subject: Constructing an object
Date: Wed, 21 Sep 2005 10:46:35 +0200
Date: 2005-09-21T10:46:35+02:00 [thread overview]
Message-ID: <dgr6lb$f2k$1@sunnews.cern.ch> (raw)
Hi,
I'm learning Ada and I would like to better understand the ways used to
create objects.
Let's say I have the following:
type Color is (Black, Red, Green, Blue, White);
type Shape is tagged record
C : Color;
end record;
type Rectangle is new Shape with record
A, B : Positive;
end record;
From what I've learnt ("Ada 95: The Craft of Object-Oriented
Programming" by John English), there are two possible ways to implement
"constructors" for these types:
1. By procedure, which is a primitive operation for each type in the
hierarchy, for example:
procedure New_Shape(C : in Color; S : out Shape) is
begin
S.C := C;
end;
procedure New_Rectangle(A, B : in Positive; C : in Color; R : out
Rectangle) is
begin
New_Shape(C, Shape(R));
R.A := A;
R.B := B;
end;
-- another version (btw - which version do you prefer?)
procedure New_Rectangle(A, B : in Positive; C : in Color; R : out
Rectangle) is
St : Shape;
begin
New_Shape(C, St);
R := (St with A => A, B => B);
end;
This does not please me much, because I can have uninitialized objects,
which may not make sense in the program:
R : Rectangle;
2. By function:
function New_Shape(C : in Color) return Shape is
S : Shape;
begin
S.C := C;
return S;
end;
function New_Rectangle(A, B : in Positive; C : in Color) return
Rectangle is
R : Rectangle;
begin
Shape(R) := New_Shape(C); -- is this OK?
R.A := A;
R.B := B;
return R;
end;
This does not please me for the same reason - no enforcement of proper
initialization, if a given type makes no sense uninitialized.
What approach do you actually use in the real (non-tutorial) code?
Are there other techniques?
(I'm aware of the controlled types, but I need to provide parameters for
construction, which the special Initialize procedure does not have.)
--
Maciej Sobczak : http://www.msobczak.com/
Programming : http://www.msobczak.com/prog/
next reply other threads:[~2005-09-21 8:46 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-21 8:46 Maciej Sobczak [this message]
2005-09-21 10:16 ` Constructing an object Georg Bauhaus
2005-09-22 7:21 ` Maciej Sobczak
2005-09-21 11:55 ` Dmitry A. Kazakov
2005-09-22 7:28 ` Maciej Sobczak
2005-09-22 7:45 ` Maciej Sobczak
2005-09-22 13:33 ` Dmitry A. Kazakov
2005-09-24 5:23 ` Randy Brukardt
2005-09-24 9:47 ` Dmitry A. Kazakov
2005-09-29 0:12 ` Randy Brukardt
2005-09-29 8:17 ` Dmitry A. Kazakov
2005-09-29 22:21 ` Randy Brukardt
2005-09-30 8:14 ` Jean-Pierre Rosen
2005-09-30 19:28 ` Dmitry A. Kazakov
2005-09-30 17:49 ` Robert A Duff
2005-10-01 0:44 ` Randy Brukardt
2005-10-01 10:49 ` Dmitry A. Kazakov
2005-10-01 11:06 ` Tapio Kelloniemi
2005-10-01 14:13 ` Robert A Duff
2005-10-02 11:52 ` Tapio Kelloniemi
2005-10-01 15:19 ` Georg Bauhaus
2005-09-23 5:40 ` Matthew Heaney
2005-09-23 7:18 ` tmoran
2005-09-23 8:23 ` Maciej Sobczak
2005-09-23 12:04 ` Dmitry A. Kazakov
2005-09-23 12:36 ` Matthew Heaney
2005-09-23 13:03 ` Hyman Rosen
2005-09-23 13:41 ` Maciej Sobczak
2005-09-23 14:23 ` Matthew Heaney
2006-01-17 6:28 ` [Offtopic] " James Dennett
2005-09-23 13:42 ` Dmitry A. Kazakov
2005-09-23 14:27 ` Matthew Heaney
2005-09-23 12:24 ` Matthew Heaney
2005-09-24 5:34 ` Randy Brukardt
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