Fix implicit access to raw pointer of scoped_refptr.

base/memory/ref_counted.h

 // 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.
 
 #ifndef BASE_MEMORY_REF_COUNTED_H_
 #define BASE_MEMORY_REF_COUNTED_H_
 
 #include <cassert>
 #include <iosfwd>
 #include <type_traits>
@@ skipping 344 matching lines @@
   void swap(T** pp) {
     T* p = ptr_;
     ptr_ = *pp;
     *pp = p;
   }
 
   void swap(scoped_refptr<T>& r) {
     swap(&r.ptr_);
   }
 
+  explicit operator bool() const { return ptr_ != nullptr; }
+
  private:

[danakj, 2016/05/10 21:37:46]

There's no reason to make a private block for this friend line.

[danakj, 2016/05/10 21:38:51]

(I'm also wondering why it's here, we're calling .get() which is public on the
<U> friend.)

[scheib, 2016/05/10 22:25:00]

Done, moved friend to bottom private section and commented why it is needed
(move constructor).

   template <typename U> friend class scoped_refptr;
 
-  // Implement "Safe Bool Idiom"
-  // https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool
-  //
-  // Allow scoped_refptr<T> to be used in boolean expressions such as
-  //   if (ref_ptr_instance)
-  // But do not become convertible to a real bool (which is dangerous).
-  //   Implementation requires:
-  //     typedef Testable
-  //     operator Testable() const
-  //     operator==
-  //     operator!=
-  //
-  // == and != operators must be declared explicitly or dissallowed, as
-  // otherwise "ptr1 == ptr2" will compile but do the wrong thing (i.e., convert
-  // to Testable and then do the comparison).
-  //
-  // C++11 provides for "explicit operator bool()", however it is currently
-  // banned due to MSVS2013. https://chromium-cpp.appspot.com/#core-blacklist
-  typedef T* scoped_refptr::*Testable;
  public:
-  operator Testable() const { return ptr_ ? &scoped_refptr::ptr_ : nullptr; }
-
   template <typename U>
   bool operator==(const scoped_refptr<U>& rhs) const {
     return ptr_ == rhs.get();
   }
 
   template <typename U>
   bool operator!=(const scoped_refptr<U>& rhs) const {
     return !operator==(rhs);
   }
 
@@ skipping 50 matching lines @@
 bool operator!=(const T* lhs, const scoped_refptr<U>& rhs) {
   return !operator==(lhs, rhs);
 }
 
 template <typename T>
 std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p) {
   return out << p.get();
 }
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_