[gambit-list] Returning struct as a value

Julian Scheid julians37 at googlemail.com
Fri Oct 9 08:27:41 EDT 2009


I think I got to the bottom of this, more or less. To answer some of
my own questions - including one from a previous mail:

> (value-Foo-1) works and (value-Foo-2) crashes. Is this expected?

Yes, a c-lambda that returns a (struct) *must* use ___alloc_rc for the
pointer that gets returned via ___result_voidstar.

c-lambdas that return (pointer anything), including (pointer
(struct)), can return arbitrary values in ___result_voidstar.

> Also: is it OK to use malloc here or am I supposed to use ___alloc_rc
> or ___C_ASSIGN_NEW ?

No, malloc is not OK. That just worked by accident. ___C_ASSIGN_NEW
and the other macros apparently can't be used in a c-declare block
(because of CPP macro nesting?) so ___alloc_rc is the right answer.

Not sure what would happen if ___USE_RC_ALLOCATION_FOR_FOREIGN got
un-defined. Could this happen or is rc-allocation-for-foreign here to
stay?

> Do I have to worry about providing code for releasing the memory allocated?

This I would still like to know, but I would suspect that I don't
since the whole point of ___alloc_rc seems to be to create a block
that can participate in Gambit memory management.

> Finally, I am curious whether there is any difference internally
> between the handling of (struct "Foo") and (type "Foo"), or is this
> just naming for the sake of clarity?

I am also still interested in an answer to this.

All this is more or less guesswork so please let me know if the above
is correct. If so, may I suggest updating the manual with this
information.


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