Align base::hash_map with C++11.

base/containers/small_map_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/containers/small_map.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <functional>
@@ skipping 396 matching lines @@
   SmallMap<hash_map<int, int> > hm;
   EXPECT_EQ(0u, hm.size());
   SmallMap<std::map<int, int> > m;
   EXPECT_EQ(0u, m.size());
 }
 
 namespace {
 
 class hash_map_add_item : public hash_map<int, int> {
  public:
-  hash_map_add_item() : hash_map<int, int>() {}

[davidben, 2014/10/02 22:38:50]

This is to work around an incredibly annoying problem with type aliases. If we
were to call it base::unordered_map, I think we would avoid this problem.

The trouble is that we're subclassing base::hash_map<int, int>. But within
base::hash_map, 'hash_map' is bound to std::hash_map. And so inside the
subclass, we inherit the parent class's binding of 'hash_map' over the one in
base. I believe this is similar why this works:

  namespace a {
  struct Foo {};
  }
  struct Bar : public a::Foo {
    Bar() : Foo() {}
  };

And this:

  namespace a {
  struct Foo {};
  typedef Foo Foo2;
  }
  struct Bar : public a::Foo2 {
    Bar() : Foo() {}
  };

But not this:

  namespace a {
  struct Foo {};
  typedef Foo Foo2;
  }
  struct Bar : public a::Foo2 {
    Bar() : Foo2() {}
  };


I'm going to leave it as-is for now since subclassing hash_map is a bizarre
thing to do, but we may want do the rename now to avoid this.

-  explicit hash_map_add_item(const std::pair<int, int>& item)
-      : hash_map<int, int>() {
+  hash_map_add_item() {}
+  explicit hash_map_add_item(const std::pair<int, int>& item) {
     insert(item);
   }
 };
 
 void InitMap(ManualConstructor<hash_map_add_item>* map_ctor) {
   map_ctor->Init(std::make_pair(0, 0));
 }
 
 class hash_map_add_item_initializer {
  public:
@@ skipping 44 matching lines @@
   EXPECT_EQ(4u, m.size());
   EXPECT_EQ(0u, m.count(-1));
 
   m[5] = 5;
   EXPECT_EQ(6u, m.size());
   // Our functor adds an extra item when we convert to a map.
   EXPECT_EQ(1u, m.count(-1));
 }
 
 }  // namespace base