/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2016 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* @author Dominik Gabi
*/
-#ifndef FOLLY_BASE_ATTRIBUTES_H_
-#define FOLLY_BASE_ATTRIBUTES_H_
+#pragma once
#ifndef __has_cpp_attribute
#define FOLLY_HAS_CPP_ATTRIBUTE(x) 0
#define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
#endif
+#ifndef __has_extension
+#define FOLLY_HAS_EXTENSION(x) 0
+#else
+#define FOLLY_HAS_EXTENSION(x) __has_extension(x)
+#endif
+
/**
* Fallthrough to indicate that `break` was left out on purpose in a switch
* statement, e.g.
#define FOLLY_FALLTHROUGH
#endif
-#endif /* FOLLY_BASE_ATTRIBUTES_H_ */
+/**
+ * Nullable indicates that a return value or a parameter may be a `nullptr`,
+ * e.g.
+ *
+ * int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) {
+ * if (*a > 0) { // safe dereference
+ * return nullptr;
+ * }
+ * if (*b < 0) { // unsafe dereference
+ * return *a;
+ * }
+ * if (b != nullptr && *b == 1) { // safe checked dereference
+ * return new int(1);
+ * }
+ * return nullptr;
+ * }
+ */
+#if FOLLY_HAS_EXTENSION(nullability)
+#define FOLLY_NULLABLE _Nullable
+#else
+#define FOLLY_NULLABLE
+#endif