+#ifdef __GNUC__
+#define MUST_CHECK_RESULT __attribute__((warn_unused_result))
+#else
+#define MUST_CHECK_RESULT
+#endif
+
+// CHECK() is like assert(), but retains any side effects no matter the compilation mode.
+#ifdef NDEBUG
+#define CHECK(x) (void)(x)
+#else
+#define CHECK(x) do { bool ok = x; if (!ok) { fprintf(stderr, "%s:%d: %s: Assertion `%s' failed.\n", __FILE__, __LINE__, __PRETTY_FUNCTION__, #x); abort(); } } while (false)
+#endif
+