[Rd] capturing value of C or Fortran function
tlumley at u.washington.edu
Mon Dec 18 18:13:34 CET 2006
On Wed, 13 Dec 2006, Harris A. Jaffee wrote:
> Re: src/main/dotcode.c:do_dotCode()
> The value, if there is one, of a function called by .C or .Fortran is not
> captured, so one needs a wrapper. To avoid that, the user would have to
> declare that there is a value, specify its type, and supply an R variable
> to hold the value. Presumably, all of these could be combined in a new
> "VALUE=var" parameter. Then do_dotCode could arrange the correct type of
> C variable to receive the value (for every one of the 66 possible instances
> of the call), and then transfer that value to 'var'.
Ick. There is no way (I hope) that .C() is going to stop being a pure
function and go and write in other variables
> It seems doable with
> a strong enough macro, if a bit complicated. Or one could say VALUE=<type>
> and get the value as a new, (n+1)_th element of the current list value.
AFAICS this is possible only for a predefined list of return types.
Even worse "vector of 4 ints" and "vector of 5 ints" count as different types,
since it is not possible for do_dotCode to work out how much memory is
pointed to by a pointer.
It seems a lot of extra code for very little extra generality. If someone
submitted a patch that also carefully documented that there was no
slowdown for .C/.Fortran and no loss of ANSI C conformance it might be
considered, but I can't predict any great enthusiasm for it.
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