Lazarus
Home
Help
TinyPortal
Search
Login
Register
Lazarus
»
Forum
»
Free Pascal
»
General
(Moderators:
FPK
,
Tomas Hajny
) »
Can a class create a class within itself?
Free Pascal
Website
Downloads
Wiki
Documentation
Bugtracker
Mailing List
Lazarus
Website
Downloads (Laz+FPC)
Packages (OPM)
FAQ
Wiki
Documentation (RTL/FCL/LCL)
Bugtracker
CCR Bugs
IRC channel
GIT
Mailing List
Other languages
Foundation
Website
Useful Wiki Links
Project Roadmap
Getting the Source
Screenshots
How to use the forum
About donations (wiki)
Bookstore
Computer Math and Games in Pascal
(preview)
Lazarus Handbook
Search
Advanced search
Recent
Offical launch of the 1 B...
by
Gustavo 'Gus' Carreno
[
Today
at 12:50:46 am]
what to do if my target M...
by
Laksen
[
Today
at 12:49:12 am]
For-in loop over constant...
by
ASerge
[
Today
at 12:36:09 am]
Converting a string/index...
by
TRon
[April 18, 2024, 11:56:37 pm]
exclude ALL packages from...
by
PascalDragon
[April 18, 2024, 11:33:29 pm]
Demoscene The Champs Crac...
by
KodeZwerg
[April 18, 2024, 11:29:50 pm]
Poll: Watches and Display...
by
440bx
[April 18, 2024, 10:55:14 pm]
Database standards OR Am ...
by
dseligo
[April 18, 2024, 10:50:26 pm]
BUG REPORT: Unable to gen...
by
PascalDragon
[April 18, 2024, 10:24:23 pm]
How to: create DLL file f...
by
paule32
[April 18, 2024, 10:23:59 pm]
Have anyone develop UEFI ...
by
PascalDragon
[April 18, 2024, 10:14:15 pm]
Lazarus for Windows on aa...
by
PascalDragon
[April 18, 2024, 10:09:10 pm]
The weird Rewrite bug
by
PascalDragon
[April 18, 2024, 09:58:53 pm]
Assign (textfile) not com...
by
PascalDragon
[April 18, 2024, 09:51:50 pm]
Question for people who h...
by
PascalDragon
[April 18, 2024, 09:44:32 pm]
Linux Workspaces -- StayO...
by
AmatCoder
[April 18, 2024, 08:34:20 pm]
I just released a commerc...
by
Seenkao
[April 18, 2024, 07:57:21 pm]
Access violation when re-...
by
TRon
[April 18, 2024, 07:37:31 pm]
[SOLVED] assembler name i...
by
TRon
[April 18, 2024, 07:26:33 pm]
A fairly simple sound sol...
by
KodeZwerg
[April 18, 2024, 07:01:52 pm]
Step-into the field sette...
by
Martin_fr
[April 18, 2024, 06:54:19 pm]
[Fun Fact] PNG and Micros...
by
Ten_Mile_Hike
[April 18, 2024, 06:24:19 pm]
HTTP/2+HTTP/1.1+WebSocket...
by
iLya2IK
[April 18, 2024, 06:14:30 pm]
Improvement of TFPTimerTh...
by
AlexTP
[April 18, 2024, 05:56:38 pm]
Arabic text, problem on L...
by
nouzi
[April 18, 2024, 05:21:27 pm]
« previous
next »
Print
Pages: [
1
]
Author
Topic: Can a class create a class within itself? (Read 826 times)
petejones
New Member
Posts: 13
Can a class create a class within itself?
«
on:
May 19, 2022, 10:37:40 pm »
Can a class create a class within itself? Here is the code:
type
TParameter = class(TObject)
private
ParamValue: Variant;
ParamType: TParameterType;
end;
type
TParameters = class
public
Items: specialize TFPGObjectList<TParameter>;
constructor Create();
procedure Add(ParameterValue: Variant; ParameterType: TParameterType);
end;
I want the TParameters class to create the Items list when an instance of the TParameters class is created. Is this possible?
Thanks
Pete
Logged
Thausand
Sr. Member
Posts: 292
Re: Can a class create a class within itself?
«
Reply #1 on:
May 19, 2022, 10:54:37 pm »
specialize:
Code: Pascal
[Select]
[+]
[-]
type
TParameterList
=
specialize TFPGObjectList<TParameter>
;
Create:
Code: Pascal
[Select]
[+]
[-]
constructor
TParameters
.
Create
;
begin
inherited
;
Items
:
=
TParameterList
.
Create
;
end
;
Free:
Code: Pascal
[Select]
[+]
[-]
destructor
TParameters
.
Destroy
;
begin
Items
.
Free
;
end
;
How to add:
Code: Pascal
[Select]
[+]
[-]
procedure
TParameters
.
Add
(
ParameterValue
:
Variant
;
ParameterType
:
TParameterType
)
;
var
Parameter
:
TParameter
;
begin
Parameter
:
=
TParameter
.
Create
;
Parameter
.
ParamValue
:
=
ParameterValue
;
Parameter
.
ParamType
:
=
ParameterType
;
Items
.
Add
(
Parameter
)
;
end
;
«
Last Edit: May 19, 2022, 11:05:33 pm by Thausand
»
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #2 on:
May 19, 2022, 11:33:32 pm »
Thanks
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #3 on:
May 20, 2022, 02:21:17 pm »
I'm getting an error to do with the constructor - when I put a breakpoint on Items:=TParameterList.Create and step over that line, Items isn't set to anything and I get a SIGSEGV error when I attempt to add to Items.
Any ideas?
«
Last Edit: May 20, 2022, 02:34:39 pm by petejones
»
Logged
howardpc
Hero Member
Posts: 4144
Re: Can a class create a class within itself?
«
Reply #4 on:
May 20, 2022, 03:52:42 pm »
My best idea is to get you to share a compilable project that gives the error.
Then others can pinpoint its cause quickly without have to guess or make assumptions about what the rest of your code might contain.
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #5 on:
May 20, 2022, 04:54:39 pm »
Good idea, I've attached a zip of the test project.
Cheers
Pete
Logged
Thausand
Sr. Member
Posts: 292
Re: Can a class create a class within itself?
«
Reply #6 on:
May 20, 2022, 05:11:07 pm »
not good:
Code: Pascal
[Select]
[+]
[-]
Parameters
.
Create
;
Parameters
.
Add
(
'Test'
,
TParameterType
.
TText
)
;
Parameters
.
Free
;
better:
Code: Pascal
[Select]
[+]
[-]
Parameters
:
=
TParameters
.
Create
;
Parameters
.
Add
(
'Test'
,
TParameterType
.
TText
)
;
Parameters
.
Free
;
Is not point you ask how to create class ? Then you forget to do
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #7 on:
May 20, 2022, 05:21:42 pm »
Ah yes, thanks!
Logged
howardpc
Hero Member
Posts: 4144
Re: Can a class create a class within itself?
«
Reply #8 on:
May 20, 2022, 05:35:58 pm »
While you can use generics, as you do, I think generics + variants is somewhat overkill.
I would simply use a TFPObjectList from contnrs unit.
Logged
Print
Pages: [
1
]
« previous
next »
Lazarus
»
Forum
»
Free Pascal
»
General
(Moderators:
FPK
,
Tomas Hajny
) »
Can a class create a class within itself?
TinyPortal
© 2005-2018