khash.h (KHASH_FOREACH): a new macro to iterate over khash table

include/mruby/khash.h

@@ -281,4 +281,24 @@ typedef const char *kh_cstr_t;
 
 MRB_END_DECL
 
+/**
+ * Macro for iterating over all elements in a khash.
+ *
+ * Usage:
+ *   KHASH_FOREACH(mrb, kh, k) {
+ *     // k is the khiter_t iterator
+ *     // Access the key with kh_key(kh, k)
+ *     // Access the value with kh_val(kh, k) if applicable
+ *     // Your code here
+ *   }
+ *
+ * @param mrb The mrb_state
+ * @param kh  The khash to iterate over
+ * @param k   The name to use for the khiter_t iterator variable
+ */
+#define KHASH_FOREACH(mrb, kh, k) \
+  if (kh) \
+    for (khiter_t k = kh_begin(kh); k != kh_end(kh); k++) \
+      if (kh_exist(kh, k))
+
 #endif  /* MRUBY_KHASH_H */