Add a macro to ignore the return value of a function.

The more typical (void)(function()) does not work with GCC when explicitly marking the -Wunused-value attribute on a function.

I plan to land the fix for bug 42904 in stages:

1) add this macro
2) fix some instance (either a misuse of release(), or just add this macro to it)
3) fix some instance (either a misuse of release(), or just add this macro to it)
....
n - 1) fix some instance (either a misuse of release(), or just add this macro to it)
n) enable the WARN_UNUSED_VALUE attribute on {scoped_ptr,scoped_ptr_malloc,scoped_array}.release()

BUG=42904
TEST=none

Review URL: http://codereview.chromium.org/1794012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@46252 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 11 insertions, 0 deletions

diff --git a/base/basictypes.h b/base/basictypes.h
index 1e44303..f6b92ec 100644
--- a/base/basictypes.h
+++ b/base/basictypes.h
@@ -327,6 +327,17 @@ inline Dest bit_cast(const Source& source) {
   return dest;
 }
 
+// Used to explicitly mark the return value of a function as unused. If you are
+// really sure you don't want to do anything with the return value of a function
+// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
+//
+//   scoped_ptr<MyType> my_var = ...;
+//   if (TakeOwnership(my_var.get()) == SUCCESS)
+//     IGNORE_RESULT(my_var.release());
+//
+#define IGNORE_RESULT(x) \
+  do { size_t unused = sizeof(x); unused = 0; } while (false)
+
 // The following enum should be used only as a constructor argument to indicate
 // that the variable has static storage class, and that the constructor should
 // do nothing to its state.  It indicates to the reader that it is legal to