Lauri Aalto wrote:
On Tue, May 6, 2008 at 5:35 PM, John Fieber <[EMAIL PROTECTED]> wrote:
That said, I do have a different problem with iterator/stream map functions
regarding contexts. The mapping function for an iterator has the signature
(rdf_iterator.h):
typedef void* (*librdf_iterator_map_handler)(librdf_iterator *iterator,
void *map_context, void *item);
The problem is the list of iterator methods you cannot call within the map
function because they produce infinite recursion:
Clearly not all of those are necessary or even appropriate to use in a map
callback since you are handed a pointer to the object, but getting the
context is relevant, and the only way to get it is to violate encapsulation
of the iterator. The stream methods exhibit the same behavior.
I'm thinking of one way to make context nodes accessible in map
functions without breaking much existing code. Introduce another
callback, say:
typedef void*
(*librdf_iterator_map_with_context_handler)(librdf_iterator *iterator,
void *map_context, void *item, void *item_context);
// (or librdf_node *item_context)
and the API function for adding them:
int librdf_iterator_add_map_with_context(librdf_iterator* iterator,
librdf_iterator_map_with_context_handler map_function,
librdf_iterator_map_free_context_handler free_context, void
*map_context);
This way the changes can be contained in the rdf_iterator class.
Neither iterator callback implementations nor iterator clients need to
be changed.
(Ditto for streams. Also maybe should try to come up with better
typedef/function names.)
Seems fine to me, but do you have a use for this? If the answer is
yes then I'd be more confident that this is the right API.
Another option would be to just change the old map function signature
and break some existing client code.
possible but there's no absolute need to do this.
Another bug that affects the iterator only is that the callback signature
is
typedef void* (*librdf_iterator_map_handler)(librdf_iterator *iterator,
void *map_context, void *item);
but it called with second two arguments swapped (rdf_iterator.c):
/* apply the map to the element */
element=map->fn(iterator, element, map->context);
I'm guessing this is wrong since the argument order is consistent in three
out of four cases: stream callback signature, stream callback call and
iterator callback signature.
Thanks. I fixed that one in svn r13842.
I guess the iterator map functions have not been used that much. This
bug has been there since 2001.
Probably true. However, the stream map functions are used to implement
various model methods such as get_targets, get_arcs when the underlying
storage only implements find_statements - the map iterator turns a
stream of statements into an iterator of nodes.
Dave
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