addition: destroy and clear

src/arraylist.c

@@ -1,6 +1,7 @@
 #include "arraylist.h"
 #include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
 
 ArrayListResult arraylist_init(size_t capacity, size_t elem_size) {
     if (capacity == 0) {
@@ -32,3 +33,28 @@ ArrayListResult arraylist_init(size_t capacity, size_t elem_size) {
 
     return (ArrayListResult) {.is_valid = true, .array = arr};
 }
+
+ArrayListErr arraylist_destroy(ArrayList *arr) {
+    if (arr == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    arr->capacity = 0;
+    arr->elem_size = 0;
+    arr->len = 0;
+    free(arr->data);
+    arr->data = NULL;
+    return ARRLIST_OK;
+}
+
+ArrayListErr arraylist_clear(ArrayList *arr) {
+    if (arr == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    memset(arr->data, 0, arr->capacity * arr->elem_size);
+    arr->capacity = 0;
+    arr->elem_size = 0;
+    arr->len = 0;
+    return ARRLIST_OK;
+}