base::ManualConstructor improvements

- use ALIGNOF macro
- use variadic templates

Review URL: https://codereview.chromium.org/1070603003

Cr-Commit-Position: refs/heads/master@{#324417}

base/memory/manual_constructor.h

@@ -18,6 +18,7 @@
 
 #include <stddef.h>
 
+#include "base/compiler_specific.h"
 #include "base/memory/aligned_memory.h"
 
 namespace base {
@@ -33,11 +34,7 @@ class ManualConstructor {
   // Support users creating arrays of ManualConstructor<>s.  This ensures that
   // the array itself has the correct alignment.
   static void* operator new[](size_t size) {
-#if defined(COMPILER_MSVC)
-    return AlignedAlloc(size, __alignof(Type));
-#else
-    return AlignedAlloc(size, __alignof__(Type));
-#endif
+    return AlignedAlloc(size, ALIGNOF(Type));
   }
   static void operator delete[](void* mem) {
     AlignedFree(mem);
@@ -56,56 +53,9 @@ class ManualConstructor {
   inline Type& operator*() { return *get(); }
   inline const Type& operator*() const { return *get(); }
 
-  // You can pass up to eight constructor arguments as arguments of Init().
-  inline void Init() {
-    new(space_.void_data()) Type;
-  }
-
-  template <typename T1>
-  inline void Init(const T1& p1) {
-    new(space_.void_data()) Type(p1);
-  }
-
-  template <typename T1, typename T2>
-  inline void Init(const T1& p1, const T2& p2) {
-    new(space_.void_data()) Type(p1, p2);
-  }
-
-  template <typename T1, typename T2, typename T3>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3) {
-    new(space_.void_data()) Type(p1, p2, p3);
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4) {
-    new(space_.void_data()) Type(p1, p2, p3, p4);
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
-                   const T5& p5) {
-    new(space_.void_data()) Type(p1, p2, p3, p4, p5);
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-            typename T6>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
-                   const T5& p5, const T6& p6) {
-    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6);
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-            typename T6, typename T7>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
-                   const T5& p5, const T6& p6, const T7& p7) {
-    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6, p7);
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-            typename T6, typename T7, typename T8>
-  inline void Init(const T1& p1, const T2& p2, const T3& p3, const T4& p4,
-                   const T5& p5, const T6& p6, const T7& p7, const T8& p8) {
-    new(space_.void_data()) Type(p1, p2, p3, p4, p5, p6, p7, p8);
+  template <typename... Ts>
+  inline void Init(const Ts&... params) {
+    new(space_.void_data()) Type(params...);
   }
 
   inline void Destroy() {
@@ -113,11 +63,7 @@ class ManualConstructor {
   }
 
  private:
-#if defined(COMPILER_MSVC)
-  AlignedMemory<sizeof(Type), __alignof(Type)> space_;
-#else
-  AlignedMemory<sizeof(Type), __alignof__(Type)> space_;
-#endif
+  AlignedMemory<sizeof(Type), ALIGNOF(Type)> space_;
 };
 
 }  // namespace base