Re: [fpc-pascal] sqldb create/free lifetime of object

[Sven Barth via fpc-pascal]

Am 12.04.2017 14:32 schrieb :
> In a way, this is a form of garbage collection or RAII sort of. And
reduces the obnoxious free's required in non garbage collected programming
languages... So it's a nice feature/trick to have ownership. But at the
same time you can think there is a memory leak since there is no
create/free pair easily visible...
>
> So you train your eyes to look for ownership.
>
> And similarly, delphi gui widgets you throw onto a form, don't need to be
freed yourself, even though the program created them - so in a way delphi
TForm's gui widgets are also garbage collected, sort of. Again a nice
feature/trick to avoid all the obnoxious free calls that bloat up the
source code with line noise.

Both are in fact using the same mechanism as you can put e.g. a
TSQLTransaction on a form as well.

Regards,
Sven
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Re: [fpc-pascal] sqldb create/free lifetime of object

[noreply]

On 2017-04-12 05:03, LacaK wrote:

Yes, example should be adjusted. Please report bug to not forget.
Thanks
-Laco.



It is not a bug, I just wanted to clarify the magic going on behind the 
scenes - which, is "ownership".


That's all I needed to know.

The key to seeing this trick/magic is in the Create function where you 
pass in the C (connection) as the owner.


But on my cell phone I didn't really see this, and, it's not always 
obvious.. hence my gripe.


In a way, this is a form of garbage collection or RAII sort of. And 
reduces the obnoxious free's required in non garbage collected 
programming languages... So it's a nice feature/trick to have ownership. 
But at the same time you can think there is a memory leak since there is 
no create/free pair easily visible...


So you train your eyes to look for ownership.

And similarly, delphi gui widgets you throw onto a form, don't need to 
be freed yourself, even though the program created them - so in a way 
delphi TForm's gui widgets are also garbage collected, sort of. Again a 
nice feature/trick to avoid all the obnoxious free calls that bloat up 
the source code with line noise.

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Re: [fpc-pascal] sqldb create/free lifetime of object

[LacaK]

Yes, example should be adjusted. Please report bug to not forget.


The example is correct. All objects are freed. No need for a bugreport.

Yes, correct.
-Laco.

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Re: [fpc-pascal] sqldb create/free lifetime of object

[Michael Van Canneyt]

On Wed, 12 Apr 2017, LacaK wrote:


Yes, example should be adjusted. Please report bug to not forget.


The example is correct. All objects are freed. No need for a bugreport.

Michael.
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Re: [fpc-pascal] sqldb create/free lifetime of object

[Michael Van Canneyt]

On Wed, 12 Apr 2017, Lars wrote:


The sql query object and transaction object are created but not freed:

http://www.freepascal.org/docs-html/fcl/sqldb/usingsqldb.html

I think the docs should mention that the objects need not to be freed, as
this violates normal programming practice of freeing all objects you
create.


They must of course be freed. They ARE freed.



P.s. how is it freed magically? Sorry I am on cell phone and cannot look
at source easily to find out


All three classes are components.
Q and T are owned by C. When C is freed, Q and T are freed.



This is one gripe I have with programming is that you never really know if
something should be freed just by looking at the code. If it is not freed
and it was created by you it is a good indication its a mem leak, but not
if there is magic behind the scenes to free it automatically


There is no magic other than standard TComponent owner/owned functionality.

Michael.
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Re: [fpc-pascal] sqldb create/free lifetime of object

[LacaK]

Yes, example should be adjusted. Please report bug to not forget.
Thanks
-Laco.


The sql query object and transaction object are created but not freed:

http://www.freepascal.org/docs-html/fcl/sqldb/usingsqldb.html

I think the docs should mention that the objects need not to be freed, as
this violates normal programming practice of freeing all objects you
create.

P.s. how is it freed magically? Sorry I am on cell phone and cannot look
at source easily to find out

This is one gripe I have with programming is that you never really know if
something should be freed just by looking at the code. If it is not freed
and it was created by you it is a good indication its a mem leak, but not
if there is magic behind the scenes to free it automatically
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