Add helpers for CGL types.

base/mac/scoped_typeref.h

Index: base/mac/scoped_typeref.h
diff --git a/base/mac/scoped_typeref.h b/base/mac/scoped_typeref.h
new file mode 100644
index 0000000000000000000000000000000000000000..21100d8ead122024bc7f3a626f0f1058cabc3435
--- /dev/null
+++ b/base/mac/scoped_typeref.h
@@ -0,0 +1,124 @@
+// 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 patterend after scoped_ptr<>, but maintains a ownership
+// of a reference to any type that is maintained by Retain and Release methods.
+//
+// For initialization with an existing object, the caller must 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.
+//
+// For the many types that have pass-by-pointer create functions, the function
+// ptr_for_init() is provided to allow direct initialization and assumption of
+// ownership of the object, e.g:
+//
+//     base::ScopedTypeRef<
+//         CGLContextObj, CGLContextObj, CGLRetainContext, CGLReleaseContext>
+//             context;
+//     CGLCreateContext(pixel_format, share_group, context.ptr_for_init());
+//
+// Note that the type taken by the Retain and Release methods, |R|, may be a
+// subtype of the type being owned, |T|, and therefore needs to be
+// parameterized separately.
+
+template<typename T, typename R, R Retain(R), void Release(R)>
+class ScopedTypeRef {
+ public:
+  typedef T element_type;
+
+  ScopedTypeRef() : object_(NULL) {}
+
+  ScopedTypeRef(
+      T object,
+      base::scoped_policy::OwnershipPolicy policy)

[Mark Mentovai, 2014/02/07 17:22:08]

Having a default policy here is kind of nice.

[ccameron, 2014/02/07 19:23:57]

I've added this back ... but I didn't like the default ownership policy (the
very first time I used it, I got it wrong).

+      : object_(object) {
+    if (object_ && policy == base::scoped_policy::RETAIN)
+      Retain(object_);
+  }
+
+  ScopedTypeRef(const ScopedTypeRef<T, R, Retain, Release>& that)
+      : object_(that.object_) {
+    if (object_)
+      Retain(object_);
+  }
+
+  virtual ~ScopedTypeRef() {
+    if (object_)
+      Release(object_);
+  }
+
+  ScopedTypeRef& operator=(const ScopedTypeRef<T, R, Retain, Release>& 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* ptr_for_init() 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)
+      Retain(object);
+    if (object_)
+      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_