Documentation/technical/api-oid-array.txt

   1 oid-array API
   2 ==============
   3
   4 The oid-array API provides storage and manipulation of sets of object
   5 identifiers. The emphasis is on storage and processing efficiency,
   6 making them suitable for large lists. Note that the ordering of items is
   7 not preserved over some operations.
   8
   9 Data Structures
  10 ---------------
  11
  12 `struct oid_array`::
  13
  14         A single array of object IDs. This should be initialized by
  15         assignment from `OID_ARRAY_INIT`.  The `oid` member contains
  16         the actual data. The `nr` member contains the number of items in
  17         the set.  The `alloc` and `sorted` members are used internally,
  18         and should not be needed by API callers.
  19
  20 Functions
  21 ---------
  22
  23 `oid_array_append`::
  24         Add an item to the set. The object ID will be placed at the end of
  25         the array (but note that some operations below may lose this
  26         ordering).
  27
  28 `oid_array_lookup`::
  29         Perform a binary search of the array for a specific object ID.
  30         If found, returns the offset (in number of elements) of the
  31         object ID. If not found, returns a negative integer. If the array
  32         is not sorted, this function has the side effect of sorting it.
  33
  34 `oid_array_clear`::
  35         Free all memory associated with the array and return it to the
  36         initial, empty state.
  37
  38 `oid_array_for_each`::
  39         Iterate over each element of the list, executing the callback
  40         function for each one. Does not sort the list, so any custom
  41         hash order is retained. If the callback returns a non-zero
  42         value, the iteration ends immediately and the callback's
  43         return is propagated; otherwise, 0 is returned.
  44
  45 `oid_array_for_each_unique`::
  46         Iterate over each unique element of the list in sorted order,
  47         but otherwise behave like `oid_array_for_each`. If the array
  48         is not sorted, this function has the side effect of sorting
  49         it.
  50
  51 `oid_array_filter`::
  52         Apply the callback function `want` to each entry in the array,
  53         retaining only the entries for which the function returns true.
  54         Preserve the order of the entries that are retained.
  55
  56 Examples
  57 --------
  58
  59 -----------------------------------------
  60 int print_callback(const struct object_id *oid,
  61                     void *data)
  62 {
  63         printf("%s\n", oid_to_hex(oid));
  64         return 0; /* always continue */
  65 }
  66
  67 void some_func(void)
  68 {
  69         struct sha1_array hashes = OID_ARRAY_INIT;
  70         struct object_id oid;
  71
  72         /* Read objects into our set */
  73         while (read_object_from_stdin(oid.hash))
  74                 oid_array_append(&hashes, &oid);
  75
  76         /* Check if some objects are in our set */
  77         while (read_object_from_stdin(oid.hash)) {
  78                 if (oid_array_lookup(&hashes, &oid) >= 0)
  79                         printf("it's in there!\n");
  80
  81         /*
  82          * Print the unique set of objects. We could also have
  83          * avoided adding duplicate objects in the first place,
  84          * but we would end up re-sorting the array repeatedly.
  85          * Instead, this will sort once and then skip duplicates
  86          * in linear time.
  87          */
  88         oid_array_for_each_unique(&hashes, print_callback, NULL);
  89 }
  90 -----------------------------------------