Add helpers for CGL types.

base/mac/scoped_typeref.h

+// Copyright 2014 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_MAC_SCOPED_TYPEREF_H_
+#define BASE_MAC_SCOPED_TYPEREF_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/logging.h"
+#include "base/memory/scoped_policy.h"
+
+namespace base {
+
+// ScopedTypeRef<> is patterned after scoped_ptr<>, but maintains a ownership
+// of a reference to any type that is maintained by Retain and Release methods.
+//
+// The Traits structure must provide the Retain and Release methods for type T.
+// A default ScopedTypeRefTraits is used but not defined, and should be defined
+// for each type to use this interface. For example, an appropriate definition
+// of ScopedTypeRefTraits for CGLContextObj would be:
+//
+//   template<>
+//   struct ScopedTypeRefTraits<CGLContextObj> {
+//     void Retain(CGLContextObj object) { CGLContextRetain(object); }
+//     void Release(CGLContextObj object) { CGLContextRelease(object); }
+//   };
+//
+// For the many types that have pass-by-pointer create functions, the function
+// InitializeInto() is provided to allow direct initialization and assumption
+// of ownership of the object. For example, continuing to use the above
+// CGLContextObj specialization:
+//
+//   base::ScopedTypeRef<CGLContextObj> context;
+//   CGLCreateContext(pixel_format, share_group, context.InitializeInto());
+//
+// For initialization with an existing object, the caller may specify whether
+// the ScopedTypeRef<> being initialized is assuming the caller's existing
+// ownership of the object (and should not call Retain in initialization) or if
+// it should not assume this ownership and must create its own (by calling
+// Retain in initialization). This behavior is based on the |policy| parameter,
+// with |ASSUME| for the former and |RETAIN| for the latter. The default policy
+// is to |ASSUME|.
+
+template<typename T>
+struct ScopedTypeRefTraits;
+
+template<typename T, typename Traits = ScopedTypeRefTraits<T>>
+class ScopedTypeRef {
+ public:
+  typedef T element_type;
+
+  ScopedTypeRef(
+      T object = NULL,
+      base::scoped_policy::OwnershipPolicy policy = base::scoped_policy::ASSUME)
+      : object_(object) {
+    if (object_ && policy == base::scoped_policy::RETAIN)
+      Traits::Retain(object_);
+  }
+
+  ScopedTypeRef(const ScopedTypeRef<T, Traits>& that)
+      : object_(that.object_) {
+    if (object_)
+      Traits::Retain(object_);
+  }
+
+  ~ScopedTypeRef() {
+    if (object_)
+      Traits::Release(object_);
+  }
+
+  ScopedTypeRef& operator=(const ScopedTypeRef<T, Traits>& that) {
+    reset(that.get(), base::scoped_policy::RETAIN);
+    return *this;
+  }
+
+  // This is to be used only to take ownership of objects that are created
+  // by pass-by-pointer create functions. To enforce this, require that the
+  // object be reset to NULL before this may be used.
+  T* InitializeInto() WARN_UNUSED_RESULT {
+    DCHECK(!object_);
+    return &object_;
+  }
+
+  void reset(T object = NULL,
+             base::scoped_policy::OwnershipPolicy policy =
+                base::scoped_policy::ASSUME) {
+    if (object && policy == base::scoped_policy::RETAIN)
+      Traits::Retain(object);
+    if (object_)
+      Traits::Release(object_);
+    object_ = object;
+  }
+
+  bool operator==(T that) const {
+    return object_ == that;
+  }
+
+  bool operator!=(T that) const {
+    return object_ != that;
+  }
+
+  operator T() const {
+    return object_;
+  }
+
+  T get() const {
+    return object_;
+  }
+
+  void swap(ScopedTypeRef& that) {
+    T temp = that.object_;
+    that.object_ = object_;
+    object_ = temp;
+  }
+
+  // ScopedTypeRef<>::release() is like scoped_ptr<>::release.  It is NOT
+  // a wrapper for Release().  To force a ScopedTypeRef<> object to call
+  // Release(), use ScopedTypeRef<>::reset().
+  T release() WARN_UNUSED_RESULT {
+    T temp = object_;
+    object_ = NULL;
+    return temp;
+  }
+
+ private:
+  T object_;
+};
+
+}  // namespace base
+
+#endif  // BASE_MAC_SCOPED_TYPEREF_H_