Either I am looking wrong (and missing the point) or the text at <http://www.freepascal.org/docs-html/ref/refse91.html> (a follow-up on <http://bugs.freepascal.org/view.php?id=26874>) is incorrect.

Doesn't the call to DoIt1(y,7) in procedure Test3 cause the reference count to be increased (from 0 to 1) and then decreased (from 1 to 0 and thus disposed) ? And doesn't DoIt1 use value parameters ? Therefore, doesn't the comment on the const case (on the top of the page) belong to the value-parameter (aka "nothing") case ? I would say, If const parameters, like var parameters, do nothing, there is no reference count decrease, therefore no dispose of classes (implementing an interface) even when the reference count is 0 ?

Regards,

Adriaan van Os

Adriaan van Os wrote on Wed, 17 Aug 2016:

Yes.

Therefore, doesn't the comment on the const case (on the top of the page) belong to the value-parameter (aka "nothing") case ?

It actually applies to both.

I would say, If const parameters, like var parameters, do nothing, there is no reference count decrease, therefore no dispose of classes (implementing an interface) even when the reference count is 0 ?

It's about when you pass reference counted non-lvalues to parameters, e.g. the result of a function or the expression "ClassInstance as InterfaceType". In that case, the compiler will create a temp (on the caller side) to store that function/expression result, which results the reference count of the interface instance to be increased. After the function call to which this interface instance has been passed as parameter returns, the reference count will be decreased again because the temp gets freed. If the reference count becomes 0 at that point, the instance gets freed too. As a result, in this case even with a "const" parameter you still have an interface instance that gets freed at some point after the call (since otherwise there would be a memory/reference count leak).

Passing a class instance directly to a const interface parameter does not result in the creation of a temp and hence does not result in reference count increases/decreases. In case of a value parameter, there is reference count on the callee side regardless of what you passed in.

Jonas

Thanks for the clarification. I suggest the doc page <http://www.freepascal.org/docs-html/ref/refse91.html> to be changed accordingly.

Regards,

Adriaan van Os

Thanks for the clarification. I suggest the doc page <http://www.freepascal.org/docs-html/ref/refse91.html> to be changed accordingly.

And also the test program there.

Regards,

Adriaan van Os

And what do you want to see changed ?
The test program shows the actual behaviour of the compiler ?

Michael.