Add once iterator

README.md

@@ -140,6 +140,7 @@ All iterators and functions below are prefixed with the name `citer_` to avoid c
 | flatten    | Flattens an iterator of iterators into a single iterator.                                                           |
 | inspect    | Calls a callback function on each item of an iterator, without modifying the returned items.                        |
 | map        | Maps each item of an iterator using a callback function.                                                            |
+| once       | Iterator which returns a given item once. Equivalent to `citer_take(citer_repeat(item), 1)`.                        |
 | over_array | Iterates over the items in an array. Returns a pointer to each item in the array as the item.                       |
 | repeat     | Iterator which repeatedly returns the same item.                                                                    |
 | skip       | Skips the first N items of another iterator.                                                                        |

src/repeat.h

@@ -23,4 +23,14 @@
 
 iterator_t *citer_repeat(void *);
 
+/*
+ * Create an iterator that yields a single item.
+ *
+ * Parameters:
+ *   item - The item to yield.
+ *
+ * The returned iterator must be freed after use with citer_free().
+ */
+#define citer_once(item) citer_take(citer_repeat(item), 1)
+
 #endif /* _CITER_REPEAT_H_ */