On 18.11.2011 18:31, AvP wrote:
1. Is this behavior intended (generic objects)?
I didn't find anything like that in the docs
It's at least not forbidden. I can imagine though that it was forgotten
to document as objects aren't used by that many persons (and thus they
are forgotten rather easily). They are rather similary handled by the
compiler as "class" (at least in regards to parsing; the code generated
is of course different).
2. Replacing "object" at (1) with "class" gives an error when compiling
Simply replacing "object" by "class" is not sufficient, because classes
need to be used differently than objects. If you need help regarding
this, I can provide you one if you want or you can read this:
http://wiki.freepascal.org/Object_Oriented_Programming_with_FreePascal_and_Lazarus
3. In my case the specialization should only work if _ResType is TType or
derived, as certain fields and functions/procedures are read / executed
Is there currently a way to do this typesafe (my version is a hack, I believe)
?
If not, maybe this would be an interesting feature for FPC.
Currently this is not possible, but I plan to add that, because of
Delphi compatibility. The feature that you want is called "constraints"
and the declaration of "TManager" will then look like this:
generic TManager<_ResType: TType> = object
...
end;
The compiler will then also be able to check whether you are using
methods that are valid for the passed type.
Regarding your code:
constructor TManager.Create;
begin
SetLength(Resource, 2);
Resource[0] := New(PResType, Init); // You need to allocate the memory
for the object
//> Resource[0]^.Init; // No problem here
WriteLn('Manager.Create done...');
end;
destructor TManager.Destroy;
begin
Dispose(Resource[0], Done); // Free the memory allocated earlier
//> Resource[0]^.Done; // No problem here
WriteLn('Manager.Destroy done...');
end;
Please note: While this is how it SHOULD work this does currently not
work with any version of the compiler except maybe my generic branch (I
haven't tested that yet).
As a workaround you can do this:
In TManager.Create:
Resource[0] := New(PResType);
Resource[0]^.Init;
In TManager.Destroy:
Resource[0]^.Dispose;
Dispose(Resource[0]);
This will issue two warnings though, but it works.
Regards,
Sven
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