8067306: Improve STATIC_ASSERT
Summary: New improved implementation
Reviewed-by: ehelin, stefank
--- a/hotspot/src/share/vm/utilities/debug.hpp Fri Jan 09 08:38:23 2015 +0100
+++ b/hotspot/src/share/vm/utilities/debug.hpp Fri Jan 09 11:33:48 2015 -0500
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -225,21 +225,22 @@
void warning(const char* format, ...) ATTRIBUTE_PRINTF(1, 2);
-#ifdef ASSERT
-// Compile-time asserts.
-template <bool> struct StaticAssert;
-template <> struct StaticAssert<true> {};
+// Compile-time asserts. Cond must be a compile-time constant expression that
+// is convertible to bool. STATIC_ASSERT() can be used anywhere a declaration
+// may appear.
+//
+// Implementation Note: STATIC_ASSERT_FAILURE<true> provides a value member
+// rather than type member that could be used directly in the typedef, because
+// a type member would require conditional use of "typename", depending on
+// whether Cond is dependent or not. The use of a value member leads to the
+// use of an array type.
-// Only StaticAssert<true> is defined, so if cond evaluates to false we get
-// a compile time exception when trying to use StaticAssert<false>.
-#define STATIC_ASSERT(cond) \
- do { \
- StaticAssert<(cond)> DUMMY_STATIC_ASSERT; \
- (void)DUMMY_STATIC_ASSERT; /* ignore */ \
- } while (false)
-#else
-#define STATIC_ASSERT(cond)
-#endif
+template<bool x> struct STATIC_ASSERT_FAILURE;
+template<> struct STATIC_ASSERT_FAILURE<true> { enum { value = 1 }; };
+
+#define STATIC_ASSERT(Cond) \
+ typedef char STATIC_ASSERT_FAILURE_ ## __LINE__ [ \
+ STATIC_ASSERT_FAILURE< (Cond) >::value ]
// out of shared space reporting
enum SharedSpaceType {