I have a really weird bug in my application, i succeeded in making a small program with the bare munimum to show that bug.

The full source code of the application + a dub.json file are at https://github.com/Begah/D_Pointer_Problem ( < 300 LOC )

I have a template called ResourceManager (asset.d) which takes in an asset ( Texture or Model ) and return a handle to it.
A handle has a pointer to the asset as well as a pointer to an integer ( referenceCounter ) both allocated by C's malloc.

First, i call ResourceManager!(Model).get("Coin.obj"). This function checks if that resource is already loaded, if not ( and in this case it's not ) then it calls model.loadModel();
A model has an array of textures, for simplicity sakes, in this example i only add one texture.
Before model.loadModel returns the struct created, i first prints the location and value of the referenceCounter of the first texture in the model :
	Logger.info(model.textures[0].referenceCount);
	Logger.info(*model.textures[0].referenceCount);
	
For example it prints :
	INFO (source\model.d|38) : 597F08     <- Location of the referenceCounter
	INFO (source\model.d|39) : 2          <- Value of the referenceCounter
	
Next, model.loadModel return the model structure to ResourceManager!(Model).get("Coin.obj") :
	AssetType asset = loadFunc(asset_name, args);

	static if(is(model.Model == AssetType)) {
		Logger.info(asset.textures[0].referenceCount);
		Logger.info(*asset.textures[0].referenceCount);
		Logger.info(asset.textures[0].referenceCount);
	}
	
And this is where my application, when ResourceManager!(Model).get("Coin.obj") prints the location and value of the first texture's referenceCounter.
This prints :
	INFO (source\assets.d|83) : 597F08    <- Location of the referenceCounter
	INFO (source\assets.d|84) : 1         <- Value of the referenceCounter
	INFO (source\assets.d|85) : 434A7C    <- Location of the referenceCounter ( again )
	
These three lines of code does nothing except prints to the console.
As you can see, for some reason, the location of the referenceCounter changes for no apparant reason.
I have done many different test and changes but i can't understand why this bug is happening, any ideas?

I can't help but notice that loadModel is not a static member function, yet you don't seem to call it with a Model object in your "get" function.

Also have a look at std.typecons.RefCounted if you want reference counted data..

On Thursday, 9 June 2016 at 19:00:42 UTC, cy wrote:
> I can't help but notice that loadModel is not a static member function, yet you don't seem to call it with a Model object in your "get" function.
>
> Also have a look at std.typecons.RefCounted if you want reference counted data..

loadModel is not a method, it is a function. Being a function it doesn't have a 'this' so doesn't need to be called with an object.
Also, i tried using std.typecons.RefCounted but i didn't like the lack of control i had over it ( refCount is private and only has a getter method ).

On Friday, 10 June 2016 at 07:28:44 UTC, Begah wrote:
> On Thursday, 9 June 2016 at 19:00:42 UTC, cy wrote:
>> I can't help but notice that loadModel is not a static member function, yet you don't seem to call it with a Model object in your "get" function.
>>
>> Also have a look at std.typecons.RefCounted if you want reference counted data..
>
> loadModel is not a method, it is a function. Being a function it doesn't have a 'this' so doesn't need to be called with an object.
> Also, i tried using std.typecons.RefCounted but i didn't like the lack of control i had over it ( refCount is private and only has a getter method ).

I have found the problem and i still don't understand why i was a problem :
struct Model
{
	TextureType[] textures;

	this(TextureType[] textures...) {
		this.textures = textures[];
	}
}

In the constructor, i copied the textures to the model's inner texture array, and for some reason this caused the problem.
So i needed to change to something like :

this.textures.length = textures.length;
foreach(i; 0..textures.length) {
	this.textures[i] = textures[i];
}

On 06/10/2016 01:32 AM, Begah wrote:

> I have found the problem and i still don't understand why i was a problem :
> struct Model
> {
>     TextureType[] textures;
>
>     this(TextureType[] textures...) {
>         this.textures = textures[];
>     }
> }

Yeah, that's a bug because the argument array is on the stack and has a short lifetime. (I wish the compiler would warn about that.) As a result, this.textures is now a reference to elements that are destroyed upon constructor exit.

I have some more explanation of it under the "Variadic function arguments have a short lifetime" section here:

  http://ddili.org/ders/d.en/parameter_flexibility.html

Ali

On Friday, 10 June 2016 at 08:32:40 UTC, Begah wrote:
> In the constructor, i copied the textures to the model's inner texture array, and for some reason this caused the problem.
> So i needed to change to something like :
>
> this.textures.length = textures.length;
> foreach(i; 0..textures.length) {
> 	this.textures[i] = textures[i];
> }

the easier one-line solution:

this.textures = textures.dup;

ooops. that solution is provided in Ali's book. sorry for the noise.