* Help on arrays of tagged types
@ 1998-01-07 0:00 mrada
1998-01-09 0:00 ` Matthew Heaney
1998-01-09 0:00 ` Stephen Leake
0 siblings, 2 replies; 6+ messages in thread
From: mrada @ 1998-01-07 0:00 UTC (permalink / raw)
Hi all,
I am racking my brains trying to figure out how to have a hetergenous
array of tagged type data. I have numerous packages all of which have
a Data type inherited from one another. I would like to declare an
array who components can point to different "Data" type objects.
Any help?
BTW: The source code would be too volumous to post here.
Chris Sparks
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Help on arrays of tagged types
1998-01-07 0:00 Help on arrays of tagged types mrada
1998-01-09 0:00 ` Matthew Heaney
@ 1998-01-09 0:00 ` Stephen Leake
1 sibling, 0 replies; 6+ messages in thread
From: Stephen Leake @ 1998-01-09 0:00 UTC (permalink / raw)
mrada wrote:
>
> Hi all,
>
> I am racking my brains trying to figure out how to have a hetergenous
> array of tagged type data. I have numerous packages all of which have
> a Data type inherited from one another. I would like to declare an
> array who components can point to different "Data" type objects.
^^^
key word; "point". Use an array of class-wide access type;
type Root_Type is abstract tagged with null record;
type Root_Access_Type is access Root_Type'class;
type Heterogenous_Array_Type is array (foo) of Root_Access_Type;
Yes, this requires allocate/deallocate; that's the price you pay for
flexibility.
If the array elements are constant, they can be staticly declared,
avoiding allocate/deallocate.
> Chris Sparks
--
- Stephe
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Help on arrays of tagged types
1998-01-07 0:00 Help on arrays of tagged types mrada
@ 1998-01-09 0:00 ` Matthew Heaney
1998-01-09 0:00 ` Matthew Heaney
1998-01-09 0:00 ` Stephen Leake
1 sibling, 1 reply; 6+ messages in thread
From: Matthew Heaney @ 1998-01-09 0:00 UTC (permalink / raw)
In article <34B37A65.607798A2@catalina-inter.net>, mrada
<mrada@CATALINA-INTER.NET> wrote:
>I am racking my brains trying to figure out how to have a hetergenous
>array of tagged type data. I have numerous packages all of which have
>a Data type inherited from one another. I would like to declare an
>array who components can point to different "Data" type objects.
You have to use indirection.
type Root_Data is tagged null record;
type Root_Data_Access_All is access all Root_Data;
type Root_Data_Array is
array (Positive range <>) of Root_Data_Access_All;
Note that use of heap is _not_ required, if you use a general access type
(as I have indicated in my example).
--------------------------------------------------------------------
Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Help on arrays of tagged types
1998-01-09 0:00 ` Matthew Heaney
@ 1998-01-09 0:00 ` Matthew Heaney
1998-01-13 0:00 ` James and Jessica Bear
0 siblings, 1 reply; 6+ messages in thread
From: Matthew Heaney @ 1998-01-09 0:00 UTC (permalink / raw)
In article <mheaney-ya023680000901982029460001@news.ni.net>, mheaney@ni.net
(Matthew Heaney) wrote:
>In article <34B37A65.607798A2@catalina-inter.net>, mrada
><mrada@CATALINA-INTER.NET> wrote:
>
>>I am racking my brains trying to figure out how to have a hetergenous
>>array of tagged type data. I have numerous packages all of which have
>>a Data type inherited from one another. I would like to declare an
>>array who components can point to different "Data" type objects.
>
>You have to use indirection.
>
>type Root_Data is tagged null record;
>
>type Root_Data_Access_All is access all Root_Data;
>
>type Root_Data_Array is
> array (Positive range <>) of Root_Data_Access_All;
>
>Note that use of heap is _not_ required, if you use a general access type
>(as I have indicated in my example).
Oops! Of course I meant
type Root_Data_Class_Access_All is access all Root_Data'Class;
type Root_Data_Array is
array (Positive range <>) of Root_Data_Class_Access_All;
--------------------------------------------------------------------
Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Help on arrays of tagged types
1998-01-09 0:00 ` Matthew Heaney
@ 1998-01-13 0:00 ` James and Jessica Bear
1998-01-13 0:00 ` Matthew Heaney
0 siblings, 1 reply; 6+ messages in thread
From: James and Jessica Bear @ 1998-01-13 0:00 UTC (permalink / raw)
[ headers snipped ]
> >>I am racking my brains trying to figure out how to have a hetergenous
> >>array of tagged type data. I have numerous packages all of which have
> >>a Data type inherited from one another. I would like to declare an
> >>array who components can point to different "Data" type objects.
> >
[ snip ]
Hello. This problem is quite similar to one I have been having also.
I am trying to create a linked list type for objects derived from a
root tagged type.
The goal is to have a homogenous Linked_List object, that stores objects
of a tagged type derived from "Root_Data". So you could set up as
follows:
Socket_List : Linked_List;
Descriptor_List : Linked_List;
etc.
The list is set up analogously to the example below, but the problem
arises
when I try to access the elements of the list. I think the problem is
that
I try to convert from "access Root_Data'Class" to "access <type derived
from Root_Data>",
which cannot work because it would entail extending the structure of the
object to the
derived type.
>
> type Root_Data_Class_Access_All is access all Root_Data'Class;
>
> type Root_Data_Array is
> array (Positive range <>) of Root_Data_Class_Access_All;
>
Should I be using generics for this instead?
Thanks for any and all help. :)
James
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Help on arrays of tagged types
1998-01-13 0:00 ` James and Jessica Bear
@ 1998-01-13 0:00 ` Matthew Heaney
0 siblings, 0 replies; 6+ messages in thread
From: Matthew Heaney @ 1998-01-13 0:00 UTC (permalink / raw)
In article <34BC054C.5DB2@peak.org>, jamesjb@peak.org wrote:
>Hello. This problem is quite similar to one I have been having also.
>I am trying to create a linked list type for objects derived from a
>root tagged type.
>
>The goal is to have a homogenous Linked_List object, that stores objects
>of a tagged type derived from "Root_Data". So you could set up as
>follows:
>
> Socket_List : Linked_List;
> Descriptor_List : Linked_List;
> etc.
>
>The list is set up analogously to the example below, but the problem
>arises
>when I try to access the elements of the list. I think the problem is
>that
>I try to convert from "access Root_Data'Class" to "access <type derived
>from Root_Data>",
>which cannot work because it would entail extending the structure of the
>object to the
>derived type.
>
>>
>> type Root_Data_Class_Access_All is access all Root_Data'Class;
>>
>> type Root_Data_Array is
>> array (Positive range <>) of Root_Data_Class_Access_All;
You want a "typeless" data structure. You'll have to downcast in that case:
declare
Descriptor_As_Data : Root_Data'Class
renames Heading (Descriptor_List).all;
File : File_Descriptor
renames File_Descriptor (Descriptor_As_Data);
begin
It's perfectly legal to downcast a class-wide object into the type you
want, because there'll be a tag check to make sure the object really is (or
is descended from) File_Descriptor.
That being said, yes, you really do want to use a generic, if the data
structure is homogeneous.
--------------------------------------------------------------------
Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271
^ permalink raw reply [flat|nested] 6+ messages in thread
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1998-01-07 0:00 Help on arrays of tagged types mrada
1998-01-09 0:00 ` Matthew Heaney
1998-01-09 0:00 ` Matthew Heaney
1998-01-13 0:00 ` James and Jessica Bear
1998-01-13 0:00 ` Matthew Heaney
1998-01-09 0:00 ` Stephen Leake
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