Merge "Add SIZEOF_MEMBER."

base/Android.bp

@@ -124,6 +124,7 @@ cc_test {
         "errors_test.cpp",
         "file_test.cpp",
         "logging_test.cpp",
+        "macros_test.cpp",
         "parsedouble_test.cpp",
         "parseint_test.cpp",
         "parsenetaddress_test.cpp",

base/include/android-base/macros.h

@@ -20,6 +20,8 @@
 #include <stddef.h>  // for size_t
 #include <unistd.h>  // for TEMP_FAILURE_RETRY
 
+#include <utility>
+
 // bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't.
 #ifndef TEMP_FAILURE_RETRY
 #define TEMP_FAILURE_RETRY(exp)            \
@@ -114,6 +116,8 @@ char(&ArraySizeHelper(T(&array)[N]))[N];  // NOLINT(readability/casting)
   ((sizeof(a) / sizeof(*(a))) / \
     static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))
 
+#define SIZEOF_MEMBER(t, f) sizeof(std::declval<t>().f)
+
 // Changing this definition will cause you a lot of pain.  A majority of
 // vendor code defines LIKELY and UNLIKELY this way, and includes
 // this header through an indirect path.

base/macros_test.cpp

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "android-base/macros.h"
+
+#include <stdint.h>
+
+#include <gtest/gtest.h>
+
+TEST(macros, SIZEOF_MEMBER_macro) {
+  struct S {
+    int32_t i32;
+    double d;
+  };
+  ASSERT_EQ(4U, SIZEOF_MEMBER(S, i32));
+  ASSERT_EQ(8U, SIZEOF_MEMBER(S, d));
+}