Guidance on FreeAndNil for Delphi noob

[David Heffernan 2402]

4 hours ago, Darian Miller said:

One step further... I worked with a Delphi developer who rarely used Free, and tried to only use Destroy.  Everyone seems to have an opinion on Free vs FreeAndNil but he was the only one that ever went further and said Destroy vs Free.  Some of the same arguments could be had for using Destroy vs Free.  (But I still use .Free)

This one is easy to debunk. Exceptions raised in a constructor then lead to exceptions in the destructor. This is the entire reason why Free exists. 

[Brandon Staggs 364]

I think this debate will never achieve any real consensus, and in the end, each of us needs to just decide what makes sense. Here's a nice fun read from 15 years ago:

 

https://blog.therealoracleatdelphi.com/2010/02/a-case-against-freeandnil_5.html

 

Interesting that Bauer and Primoz take opposite sides.

[Anders Melander 1946]

20 hours ago, Brandon Staggs said:

Interesting that Bauer and Primoz take opposite sides.

I can't see that they do.

 

Here's the TLDR as I read it:

Allen is saying that you shouldn't (mindless or not) use FreeAndNil to solve logic/design bugs and AFAICT nobody is disagreeing with that.

Primoz and David are saying that they are using it to find stale reference bugs.

 

Allen's suggestion to use a debug memory manager instead isn't valid because you can't do that on a production system, as Primoz also points out.

Edited February 28 by Anders Melander

[GabrielMoraru 32]

On 2/21/2025 at 5:45 PM, Paul Dardeau said:

Embarcadero hosted a youtube livestream the other day with MVPs.

Where the hell is the link to that video. I wanted for over an year now to see that video. It was never released!

 

Google does not know such video:

https://www.google.com/search?client=firefox-b-d&q=free+and+nil+the+great+debate

Edited March 4 by GabrielMoraru

[DelphiUdIT 218]

Nothing ..... wrong replay

 

Edited March 4 by DelphiUdIT

[Lajos Juhász 316]

Just now, GabrielMoraru said:

Where the hell is the link to that video. I wanted for over an year now to see that video. It was never released!

 

 

[GabrielMoraru 32]

My "3" cents:

1. FreeAndNil will definitively help you if you have stale pointers.

2. FreeAndNil costs only few more CPU cycles compared to Free().

3. Some people with big mouth 🙂 suggested that FreeAndNil could be bad (somehow magically it will break your code), BUT nobody was able to post a piece of compilable code to prove it 🙂 . Until they do, they remain "big mouth" 🙂 . [Yes, this is a challenge]

 

But, yes, don't design your code architecture around it.

 

_

 

That being said, since it is so cheap to use it and might bring benefits, I do use it.

 

PS: There were cases where it really helped. 

For example I had problems with a "use after free" in the ccrExif library. They were using an object after free. Replacing all .Free with FreeAndNil "magically" solved the "mystery". 

Edited March 4 by GabrielMoraru