Eliminate HICON leaks caused by creating icons from bitmap image.

base/win/scoped_gdi_object.h

 // Copyright (c) 2010 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.
 
 #ifndef BASE_WIN_SCOPED_GDI_OBJECT_H_
 #define BASE_WIN_SCOPED_GDI_OBJECT_H_
 
 #include <windows.h>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
+#include "base/move.h"
 
 namespace base {
 namespace win {
 
 // Like ScopedHandle but for GDI objects.
 template<class T>
 class ScopedGDIObject {

[grt (UTC plus 2), 2015/11/06 19:49:20]

can you implement this in terms of ScopedGeneric? it seems odd that the original
commit message for SG mentions ScopedGDIObject as a candidate for using it, yet
it doesn't.

[anpol, 2015/11/06 20:28:16]

Looking at ScopedGeneric briefly:

* ScopedGDIObject defines Get/Set while ScopedGeneric defines get/reset.
* ScopedGDIObject defines implicit conversion to/from handle type,
  while ScopedGeneric makes conversion explicit and defines == and !=
  for convenience.

Simply replacing ScopedGDIObject with ScopedGeneric would break existing code
that relies on 'base' library. While we can fix Chromium code, there are other
projects too. Any suggestions?

+  MOVE_ONLY_TYPE_WITH_MOVE_CONSTRUCTOR_FOR_CPP_03(ScopedGDIObject)
+
  public:
-  ScopedGDIObject() : object_(NULL) {}
+  ScopedGDIObject() : object_(nullptr) {}
+  ScopedGDIObject(decltype(nullptr)) : object_(nullptr) {}
+
+  // Constructor that takes ownership of an object.
   explicit ScopedGDIObject(T object) : object_(object) {}
 
+  // Constructor that transfers ownership from another ScopedGDIObject.
+  ScopedGDIObject(ScopedGDIObject&& other) : object_(nullptr) {
+    Set(other.release());
+  }
+
   ~ScopedGDIObject() {
     Close();
   }
 
   T Get() {
     return object_;
   }
 
   void Set(T object) {
     if (object_ && object != object_)
       Close();
     object_ = object;
   }
 
+  // operator= that deletes the currently owned object, if any.
+  ScopedGDIObject& operator=(decltype(nullptr)) {
+    Set(nullptr);
+    return *this;
+  }
+
+  // operator= that takes ownership of an object.
   ScopedGDIObject& operator=(T object) {
     Set(object);
     return *this;
   }
 
+  // operator= that transfers ownership from another ScopedGDIObject.
+  ScopedGDIObject& operator=(ScopedGDIObject&& rhs) {
+    Set(rhs.release());
+    return *this;
+  }
+
   T release() {
     T object = object_;
-    object_ = NULL;
+    object_ = nullptr;
     return object;
   }
 
   operator T() { return object_; }
 
  private:
   void Close() {
     if (object_)
       DeleteObject(object_);
   }
 
   T object_;
-  DISALLOW_COPY_AND_ASSIGN(ScopedGDIObject);
 };
 
 // An explicit specialization for HICON because we have to call DestroyIcon()
 // instead of DeleteObject() for HICON.
 template<>
 void inline ScopedGDIObject<HICON>::Close() {
   if (object_)
     DestroyIcon(object_);
 }
 
 // Typedefs for some common use cases.
 typedef ScopedGDIObject<HBITMAP> ScopedBitmap;
 typedef ScopedGDIObject<HRGN> ScopedRegion;
 typedef ScopedGDIObject<HFONT> ScopedHFONT;
 typedef ScopedGDIObject<HICON> ScopedHICON;
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_SCOPED_GDI_OBJECT_H_