1 files changed, 57 insertions, 0 deletions
diff --git a/misc/examples/priorityqueues/functor.c b/misc/examples/priorityqueues/functor.c
new file mode 100644
index 00000000..e3bde1dd
--- /dev/null
+++ b/misc/examples/priorityqueues/functor.c
@@ -0,0 +1,57 @@
+// Implements c++ example: https://en.cppreference.com/w/cpp/container/priority_queue
+// Example of per-instance less-function on a single priority queue type
+//
+
+#include <stdio.h>
+
+#define i_type IPQue
+#define i_base cpque
+#define i_key int
+#define i_extend bool(*less)(const int*, const int*);
+#define i_less(x, y) c_extend()->less(x, y)
+// Note: i_less: c_extend() accessible for cpque types
+//       i_cmp: c_extend() accessible for csmap and csset types
+//       i_hash/i_eq: c_extend() accessible for cmap and cset types
+#include <stc/extend.h>
+
+void print_queue(const char* name, IPQue_ext q) {
+    // NB: make a clone because there is no way to traverse
+    // priority queue's content without erasing the queue.
+    IPQue_ext copy = {q.less, IPQue_clone(q.get)};
+    
+    for (printf("%s: \t", name); !IPQue_empty(&copy.get); IPQue_pop(&copy.get))
+        printf("%d ", *IPQue_top(&copy.get));
+    puts("");
+
+    IPQue_drop(&copy.get);
+}
+
+static bool int_less(const int* x, const int* y) { return *x < *y; }
+static bool int_greater(const int* x, const int* y) { return *x > *y; }
+static bool int_lambda(const int* x, const int* y) { return (*x ^ 1) < (*y ^ 1); }
+
+int main(void)
+{
+    const int data[] = {1,8,5,6,3,4,0,9,7,2}, n = c_arraylen(data);
+    printf("data: \t");
+    c_forrange (i, n) printf("%d ", data[i]);
+    puts("");
+
+
+    // Max priority queue
+    IPQue_ext q1 = {.less=int_less};
+    IPQue_put_n(&q1.get, data, n);
+    print_queue("q1", q1);
+
+    // Min priority queue
+    IPQue_ext minq1 = {.less=int_greater};
+    IPQue_put_n(&minq1.get, data, n);
+    print_queue("minq1", minq1);
+
+    // Using lambda to compare elements.
+    IPQue_ext q5 = {.less=int_lambda};
+    IPQue_put_n(&q5.get, data, n);
+    print_queue("q5", q5);
+
+    c_drop(IPQue, &q1.get, &minq1.get, &q5.get);
+}