Move base to DEPS

base/callback_internal.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.
-
-// This file contains utility functions and classes that help the
-// implementation, and management of the Callback objects.
-
-#ifndef BASE_CALLBACK_INTERNAL_H_
-#define BASE_CALLBACK_INTERNAL_H_
-
-#include <stddef.h>
-
-#include "base/atomic_ref_count.h"
-#include "base/base_export.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/template_util.h"
-
-template <typename T>
-class ScopedVector;
-
-namespace base {
-namespace internal {
-class CallbackBase;
-
-// BindStateBase is used to provide an opaque handle that the Callback
-// class can use to represent a function object with bound arguments.  It
-// behaves as an existential type that is used by a corresponding
-// DoInvoke function to perform the function execution.  This allows
-// us to shield the Callback class from the types of the bound argument via
-// "type erasure."
-// At the base level, the only task is to add reference counting data. Don't use
-// RefCountedThreadSafe since it requires the destructor to be a virtual method.
-// Creating a vtable for every BindState template instantiation results in a lot
-// of bloat. Its only task is to call the destructor which can be done with a
-// function pointer.
-class BindStateBase {
- protected:
-  explicit BindStateBase(void (*destructor)(BindStateBase*))
-      : ref_count_(0), destructor_(destructor) {}
-  ~BindStateBase() = default;
-
- private:
-  friend class scoped_refptr<BindStateBase>;
-  friend class CallbackBase;
-
-  void AddRef();
-  void Release();
-
-  AtomicRefCount ref_count_;
-
-  // Pointer to a function that will properly destroy |this|.
-  void (*destructor_)(BindStateBase*);
-
-  DISALLOW_COPY_AND_ASSIGN(BindStateBase);
-};
-
-// Holds the Callback methods that don't require specialization to reduce
-// template bloat.
-class BASE_EXPORT CallbackBase {
- public:
-  CallbackBase(const CallbackBase& c);
-  CallbackBase& operator=(const CallbackBase& c);
-
-  // Returns true if Callback is null (doesn't refer to anything).
-  bool is_null() const { return bind_state_.get() == NULL; }
-
-  // Returns the Callback into an uninitialized state.
-  void Reset();
-
- protected:
-  // In C++, it is safe to cast function pointers to function pointers of
-  // another type. It is not okay to use void*. We create a InvokeFuncStorage
-  // that that can store our function pointer, and then cast it back to
-  // the original type on usage.
-  typedef void(*InvokeFuncStorage)(void);
-
-  // Returns true if this callback equals |other|. |other| may be null.
-  bool Equals(const CallbackBase& other) const;
-
-  // Allow initializing of |bind_state_| via the constructor to avoid default
-  // initialization of the scoped_refptr.  We do not also initialize
-  // |polymorphic_invoke_| here because doing a normal assignment in the
-  // derived Callback templates makes for much nicer compiler errors.
-  explicit CallbackBase(BindStateBase* bind_state);
-
-  // Force the destructor to be instantiated inside this translation unit so
-  // that our subclasses will not get inlined versions.  Avoids more template
-  // bloat.
-  ~CallbackBase();
-
-  scoped_refptr<BindStateBase> bind_state_;
-  InvokeFuncStorage polymorphic_invoke_;
-};
-
-// A helper template to determine if given type is non-const move-only-type,
-// i.e. if a value of the given type should be passed via .Pass() in a
-// destructive way.
-template <typename T> struct IsMoveOnlyType {
-  template <typename U>
-  static YesType Test(const typename U::MoveOnlyTypeForCPP03*);
-
-  template <typename U>
-  static NoType Test(...);
-
-  static const bool value = sizeof((Test<T>(0))) == sizeof(YesType) &&
-                            !is_const<T>::value;
-};
-
-// Returns |Then| as SelectType::Type if |condition| is true. Otherwise returns
-// |Else|.
-template <bool condition, typename Then, typename Else>
-struct SelectType {
-  typedef Then Type;
-};
-
-template <typename Then, typename Else>
-struct SelectType<false, Then, Else> {
-  typedef Else Type;
-};
-
-template <typename>
-struct CallbackParamTraitsForMoveOnlyType;
-
-template <typename>
-struct CallbackParamTraitsForNonMoveOnlyType;
-
-// TODO(tzik): Use a default parameter once MSVS supports variadic templates
-// with default values.
-// http://connect.microsoft.com/VisualStudio/feedbackdetail/view/957801/compilation-error-with-variadic-templates
-//
-// This is a typetraits object that's used to take an argument type, and
-// extract a suitable type for storing and forwarding arguments.
-//
-// In particular, it strips off references, and converts arrays to
-// pointers for storage; and it avoids accidentally trying to create a
-// "reference of a reference" if the argument is a reference type.
-//
-// This array type becomes an issue for storage because we are passing bound
-// parameters by const reference. In this case, we end up passing an actual
-// array type in the initializer list which C++ does not allow.  This will
-// break passing of C-string literals.
-template <typename T>
-struct CallbackParamTraits
-    : SelectType<IsMoveOnlyType<T>::value,
-         CallbackParamTraitsForMoveOnlyType<T>,
-         CallbackParamTraitsForNonMoveOnlyType<T> >::Type {
-};
-
-template <typename T>
-struct CallbackParamTraitsForNonMoveOnlyType {
-  typedef const T& ForwardType;
-  typedef T StorageType;
-};
-
-// The Storage should almost be impossible to trigger unless someone manually
-// specifies type of the bind parameters.  However, in case they do,
-// this will guard against us accidentally storing a reference parameter.
-//
-// The ForwardType should only be used for unbound arguments.
-template <typename T>
-struct CallbackParamTraitsForNonMoveOnlyType<T&> {
-  typedef T& ForwardType;
-  typedef T StorageType;
-};
-
-// Note that for array types, we implicitly add a const in the conversion. This
-// means that it is not possible to bind array arguments to functions that take
-// a non-const pointer. Trying to specialize the template based on a "const
-// T[n]" does not seem to match correctly, so we are stuck with this
-// restriction.
-template <typename T, size_t n>
-struct CallbackParamTraitsForNonMoveOnlyType<T[n]> {
-  typedef const T* ForwardType;
-  typedef const T* StorageType;
-};
-
-// See comment for CallbackParamTraits<T[n]>.
-template <typename T>
-struct CallbackParamTraitsForNonMoveOnlyType<T[]> {
-  typedef const T* ForwardType;
-  typedef const T* StorageType;
-};
-
-// Parameter traits for movable-but-not-copyable scopers.
-//
-// Callback<>/Bind() understands movable-but-not-copyable semantics where
-// the type cannot be copied but can still have its state destructively
-// transferred (aka. moved) to another instance of the same type by calling a
-// helper function.  When used with Bind(), this signifies transferal of the
-// object's state to the target function.
-//
-// For these types, the ForwardType must not be a const reference, or a
-// reference.  A const reference is inappropriate, and would break const
-// correctness, because we are implementing a destructive move.  A non-const
-// reference cannot be used with temporaries which means the result of a
-// function or a cast would not be usable with Callback<> or Bind().
-template <typename T>
-struct CallbackParamTraitsForMoveOnlyType {
-  typedef T ForwardType;
-  typedef T StorageType;
-};
-
-// CallbackForward() is a very limited simulation of C++11's std::forward()
-// used by the Callback/Bind system for a set of movable-but-not-copyable
-// types.  It is needed because forwarding a movable-but-not-copyable
-// argument to another function requires us to invoke the proper move
-// operator to create a rvalue version of the type.  The supported types are
-// whitelisted below as overloads of the CallbackForward() function. The
-// default template compiles out to be a no-op.
-//
-// In C++11, std::forward would replace all uses of this function.  However, it
-// is impossible to implement a general std::forward with C++11 due to a lack
-// of rvalue references.
-//
-// In addition to Callback/Bind, this is used by PostTaskAndReplyWithResult to
-// simulate std::forward() and forward the result of one Callback as a
-// parameter to another callback. This is to support Callbacks that return
-// the movable-but-not-copyable types whitelisted above.
-template <typename T>
-typename enable_if<!IsMoveOnlyType<T>::value, T>::type& CallbackForward(T& t) {
-  return t;
-}
-
-template <typename T>
-typename enable_if<IsMoveOnlyType<T>::value, T>::type CallbackForward(T& t) {
-  return t.Pass();
-}
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_CALLBACK_INTERNAL_H_