I am trying to create an SML binding to a C function that returns an
array that the caller must free. Usually, there is a free function that
takes just the array (as a pointer) which can be attached as a finalizer
with CInterface.setFinal. I have encountered a case [1] where the
caller must also pass the size of the array, returned when the array is
created, to the free function.
Simplifying the example, we have, for some C type Elem:
Elem *new (..., int *n_elems); /* n_elems is an 'out' parameter */
void free (Elem *elems, int n_elems);
and want an SML function like
val new : ... -> elem vector
Unfortunately, the function given to CInterface.setFinal is called with
only one argument, the vol that is being finalized. Therefore this free
function cannot be used. Does the current FFI architecture allow a
variant of setFinal that passes extra arguments to the finalization
function? For example:
val setFinal1 : sym -> 'a Conversion -> vol -> 'a -> unit
This isn't particularly common so is probably not a show-stopper.
Another benefit could be enabling use of functions g_slice_alloc and
g_slice_free1 that needs the number of bytes to free:
https://developer.gnome.org/glib/stable/glib-Memory-Slices.html
Thanks,
Phil
1. The C function in question is gtk_target_table_new_from_list that
returns an array and its size. The array should be freed with
gtk_target_table_free which should be passed the size. See:
-
https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-table-new-from-list
-
https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-table-free
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