Remove implicit scoped_refptr operator T*

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 "base/atomic_ref_count.h"
@@ skipping 231 matching lines @@
   scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
     if (ptr_)
       ptr_->AddRef();
   }
 
   ~scoped_refptr() {
     if (ptr_)
       ptr_->Release();
   }
 
+  // Allow scoped_refptr<T> to be used in boolean expressions, but not
+  // implicitly convertible to a real bool (which is dangerous).
+  typedef T* scoped_refptr::*Testable;
+  operator Testable() const { return ptr_ ? &scoped_refptr::ptr_ : NULL; }
+
   T* get() const { return ptr_; }
-  operator T*() const { return ptr_; }
   T* operator->() const {
     assert(ptr_ != NULL);
     return ptr_;
   }
 
   // Release a pointer.
   // The return value is the current pointer held by this object.
   // If this object holds a NULL pointer, the return value is NULL.
   // After this operation, this object will hold a NULL pointer,
   // and will not own the object any more.
@@ skipping 38 matching lines @@
 };
 
 // Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
 // having to retype all the template arguments
 template <typename T>
 scoped_refptr<T> make_scoped_refptr(T* t) {
   return scoped_refptr<T>(t);
 }
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_