From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: [announcement] SYSAPI and SYSSVC for Windows
Date: Sun, 21 Dec 2003 14:42:09 +0100
Date: 2003-12-21T14:42:09+01:00 [thread overview]
Message-ID: <bs47jo$9e9ea$1@ID-77047.news.uni-berlin.de> (raw)
In-Reply-To: bs29a5$d6n$1@online.de
Ekkehard Morgenstern wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:
>> The problem is to tell the customers, that *their* applications should be
>> designed so that *our* DLLs and hardware drivers would not stray into an
>> unpredictable state.
>
> What's the problem communicating this to the customer?
We are not MS, to tell customers, that they are wrong. (:-))
>> > C++ is well-defined also, btw. There's already a number of ISO
>> > standards for C and C++,
>>
>> A *number of* standards, fascinating! (:-))
>
> For Ada, there's also an '83 and a '95 rationale. ;)
Ada 95 practically includes Ada 83, with very minor exceptions. Rationale is
not the standard, it is rather comments to the standard. BTW, there is also
AARM - Annotated Ada Reference Manual.
>> Come on! C++ does not have:
>>
>> 1. multiple dispatch;
>
> True, except for constructors and destructors. They're always called for
> all derived classes of an object.
This is not multiple dispatch. MD is when, for example:
type Matrix is tagged ...;
function "+" (X, Y : Matrix) return Matrix;
-- This is dispatching in X, Y and the result
In C++ only one (hidden) parameter can be dispatching. All others are
contravariant, which leads to numerous nasty pitfalls
>> 3. dispatch on access types;
>
> False. Method overloading based on parameters of different types, even
> pointer types, is supported.
Overloading, not overriding. In C++:
class X {...};
void f(X * Ptr); // This is not a member of X!
Formally f is not dispatching in Ptr. It is class-wide. Compare it with Ada;
type X is tagged ...
procedure F1 (Object : access X); -- This is a "member"
procedure F2 (Object : access X'Class); -- This is not
type Y is new X with ...
procedure F1 (Object : access Y); -- This overrides F1
procedure F2 (Object : access Y'Class); -- This overloads F2
>> 4. differentiation between class-wide and specific types;
>
> Class-wide types in Ada roughly correspond to base classes in C++.
No. A class-wide type is a closure of the derived types. C++ tries to
equalize specific and class-wide types. The price is that C++ never become
a fully OO langauge, while Ada can do it easily. It possible to make all
types in Ada "tagged", even Boolean.
>> 5. functions returning class-wide objects on the stack;
>
> True, but you can return a reference to an object. (I'm not sure if
> passing a reference to a temporary object would work)
This won't help, because of 4. The same type name is sometimes denotes
class-wide, sometimes specific in C++. In declarations it is always
specific, so you cannot do:
declare
X : Object'Class := Get_From_File; -- Any descendant of Object
To achive same effect, you have to use the heap:
X_Ptr * Object = Get_From_File (); // internally calls new
...
free (X_Ptr); // do not forget to release it
>> 7. formal derived type parameter for generics;
>
> False. Of course you can use derived classes or other types in templates.
Georg Bauhaus has answered this
>> Why? The following is OK:
>>
>> type T is limited private;
>> private
>> type T is limited record
>> I : aliased Integer;
>
> Yes, but I is an Integer. Discrete types can always be aliased.
>
> In my case, it was an array of aliased types, and I wanted to create an
> access to an array element.
>> "Aliased" is the keyword for that. Objects of some types are always
>> aliased:
>>
>> type T is tagged limited ...;
>
> so I could've just used a tagged limited record?
>
> Like this:
>
> type T is tagged limited
> record
> A : My_Array_Type;
> end record;
>
> procedure F ( O : in out T ) is
> Ptr : My_Array_Cell_Ptr;
> begin
> Ptr := O.A(1)'Access;
> end;
>
> Right?
No. It is unrelated. The thing you are getting access of has to be aliased.
So it is the array elements which has to be, for example:
type T is limited private;
private
type Integer_Array is array (Integer range <>) of aliased Integer;
type T is limited record
A : Integer_Array (1..3);
end record;
procedure F (O : in out T ) is
begin
... O.A(1)'Access; -- This is OK, A(i) are aliased
end;
If the array elements be tagged, then you would need not write "aliased" in
the array declaration.
--
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de
next prev parent reply other threads:[~2003-12-21 13:42 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-12-17 19:17 [announcement] SYSAPI and SYSSVC for Windows amado.alves
2003-12-17 19:56 ` Georg Bauhaus
2003-12-18 9:08 ` Dmitry A. Kazakov
2003-12-18 12:14 ` Ekkehard Morgenstern
2003-12-18 13:31 ` Georg Bauhaus
2003-12-19 10:45 ` Ekkehard Morgenstern
2003-12-19 17:12 ` Georg Bauhaus
2003-12-19 17:22 ` Vinzent 'Gadget' Hoefler
2003-12-20 0:21 ` Ekkehard Morgenstern
2003-12-20 2:18 ` Georg Bauhaus
2003-12-20 4:40 ` Ekkehard Morgenstern
2003-12-21 3:45 ` Georg Bauhaus
2003-12-21 19:01 ` Piracy was " Robert I. Eachus
2003-12-18 14:32 ` Dmitry A. Kazakov
2003-12-19 11:11 ` Ekkehard Morgenstern
2003-12-19 15:15 ` Hyman Rosen
2003-12-19 15:50 ` Ekkehard Morgenstern
2003-12-19 16:48 ` Hyman Rosen
2003-12-19 16:57 ` Hyman Rosen
2003-12-20 1:17 ` Ekkehard Morgenstern
2003-12-21 2:19 ` Hyman Rosen
2003-12-21 10:34 ` Ekkehard Morgenstern
2003-12-22 9:02 ` Hyman Rosen
2003-12-22 15:17 ` Ekkehard Morgenstern
2003-12-22 15:08 ` Hyman Rosen
2003-12-22 15:31 ` Ekkehard Morgenstern
2003-12-22 16:35 ` Ekkehard Morgenstern
2003-12-23 1:47 ` Hyman Rosen
2003-12-23 8:40 ` Ekkehard Morgenstern
2003-12-23 9:05 ` Stephen Leake
2003-12-19 17:06 ` Dmitry A. Kazakov
2003-12-20 1:49 ` Ekkehard Morgenstern
2003-12-20 11:13 ` Dmitry A. Kazakov
2003-12-20 13:40 ` Ekkehard Morgenstern
2003-12-20 17:21 ` Dmitry A. Kazakov
2003-12-20 19:52 ` Ekkehard Morgenstern
2003-12-21 4:24 ` Georg Bauhaus
2003-12-21 13:42 ` Dmitry A. Kazakov [this message]
2003-12-21 15:48 ` Ekkehard Morgenstern
2003-12-21 17:46 ` Michal Morawski
2003-12-21 18:05 ` Ekkehard Morgenstern
2003-12-22 0:50 ` Robert I. Eachus
2003-12-23 23:02 ` Robert A Duff
2003-12-24 11:20 ` Dmitry A. Kazakov
2003-12-24 16:57 ` Robert A Duff
2003-12-25 14:00 ` Dmitry A. Kazakov
2003-12-28 1:49 ` Dave Thompson
-- strict thread matches above, loose matches on Subject: below --
2003-12-15 14:18 Ekkehard Morgenstern
2003-12-15 15:10 ` Ekkehard Morgenstern
2003-12-15 17:10 ` Jeffrey Carter
2003-12-15 18:38 ` Ekkehard Morgenstern
2003-12-16 0:25 ` Stephen Leake
2003-12-16 0:56 ` Ekkehard Morgenstern
2003-12-16 2:47 ` Ludovic Brenta
2003-12-16 17:45 ` Ekkehard Morgenstern
2003-12-16 19:54 ` Ludovic Brenta
2003-12-16 22:09 ` Ekkehard Morgenstern
2003-12-17 15:24 ` Ludovic Brenta
2003-12-17 23:23 ` Ekkehard Morgenstern
2003-12-19 18:14 ` Warren W. Gay VE3WWG
2003-12-16 5:36 ` tmoran
2003-12-16 17:30 ` Ekkehard Morgenstern
2003-12-15 20:44 ` David Marceau
2003-12-16 0:34 ` Ekkehard Morgenstern
2003-12-17 12:05 ` Dmitry A. Kazakov
2003-12-17 15:00 ` Ekkehard Morgenstern
2003-12-20 19:24 ` Ekkehard Morgenstern
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