addition: added pop_back, remove_at, pop_front

Same thing as with addtition, not tested and decided O(n)

src/arraylist.c

@@ -188,4 +188,102 @@ ArrayListErr arraylist_insert(ArrayList *arr, size_t index, void *data) {
     return ARRLIST_OK;
 }
 
+ArrayListErr arraylist_pop_back(ArrayList *arr, void *out) {
+    if (arr == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (arr->len < 1) {
+        return ARRLIST_EMPTY;
+    }
+
+    if (arr->capacity / 4 > arr->len) {
+        ArrayListErr err = arraylist_shrink(arr);
+        if (err != ARRLIST_OK) {
+            return err;
+        }
+    }
+
+    if (out != NULL) {
+        memcpy(
+            out,
+            arr->buffer + (arr->len - 1) * arr->elem_size,
+            arr->elem_size);
+    }
+
+    arr->len--;
+
+    return ARRLIST_OK;
+}
+
+ArrayListErr arraylist_pop_front(ArrayList *arr, void *out) {
+    if (arr == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (arr->len < 1) {
+        return ARRLIST_EMPTY;
+    }
+
+    if (arr->capacity / 4 > arr->len) {
+        ArrayListErr err = arraylist_shrink(arr);
+        if (err != ARRLIST_OK) {
+            return err;
+        }
+    }
+
+    if (out != NULL) {
+        memcpy(
+            out,
+            arr->buffer,
+            arr->elem_size
+        );
+    }
+
+    for (size_t i = 0; i < arr->len; i++) {
+        memcpy(
+            arr->buffer + (i * arr->elem_size),
+            arr->buffer + ((i + 1) * arr->elem_size),
+            arr->elem_size);
+    }
+
+    arr->len--;
+
+    return ARRLIST_OK;
+}
+
+ArrayListErr arraylist_remove_at(ArrayList *arr, size_t index, void *out) {
+    if (arr == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (index >= arr->len) {
+        return ARRLIST_OUT_OF_BOUNDS;
+    }
+
+    if (arr->len < 1) {
+        return ARRLIST_OK;
+    }
+
+    if (out != NULL) {
+        memcpy(
+            out,
+            arr->buffer + (index * arr->elem_size),
+            arr->elem_size
+        );
+    }
+
+    for (size_t i = index; i < arr->len; i++) {
+        memcpy(
+            arr->buffer + (index * arr->elem_size),
+            arr->buffer + ((i + 1) * arr->elem_size),
+            arr->elem_size
+        );
+    }
+
+    arr->len--;
+
+    return ARRLIST_OK;
+}
+