Move base to DEPS

base/bind_helpers.h

-// Copyright (c) 2011 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 defines a set of argument wrappers and related factory methods that
-// can be used specify the refcounting and reference semantics of arguments
-// that are bound by the Bind() function in base/bind.h.
-//
-// It also defines a set of simple functions and utilities that people want
-// when using Callback<> and Bind().
-//
-//
-// ARGUMENT BINDING WRAPPERS
-//
-// The wrapper functions are base::Unretained(), base::Owned(), base::Passed(),
-// base::ConstRef(), and base::IgnoreResult().
-//
-// Unretained() allows Bind() to bind a non-refcounted class, and to disable
-// refcounting on arguments that are refcounted objects.
-//
-// Owned() transfers ownership of an object to the Callback resulting from
-// bind; the object will be deleted when the Callback is deleted.
-//
-// Passed() is for transferring movable-but-not-copyable types (eg. scoped_ptr)
-// through a Callback. Logically, this signifies a destructive transfer of
-// the state of the argument into the target function.  Invoking
-// Callback::Run() twice on a Callback that was created with a Passed()
-// argument will CHECK() because the first invocation would have already
-// transferred ownership to the target function.
-//
-// ConstRef() allows binding a constant reference to an argument rather
-// than a copy.
-//
-// IgnoreResult() is used to adapt a function or Callback with a return type to
-// one with a void return. This is most useful if you have a function with,
-// say, a pesky ignorable bool return that you want to use with PostTask or
-// something else that expect a Callback with a void return.
-//
-// EXAMPLE OF Unretained():
-//
-//   class Foo {
-//    public:
-//     void func() { cout << "Foo:f" << endl; }
-//   };
-//
-//   // In some function somewhere.
-//   Foo foo;
-//   Closure foo_callback =
-//       Bind(&Foo::func, Unretained(&foo));
-//   foo_callback.Run();  // Prints "Foo:f".
-//
-// Without the Unretained() wrapper on |&foo|, the above call would fail
-// to compile because Foo does not support the AddRef() and Release() methods.
-//
-//
-// EXAMPLE OF Owned():
-//
-//   void foo(int* arg) { cout << *arg << endl }
-//
-//   int* pn = new int(1);
-//   Closure foo_callback = Bind(&foo, Owned(pn));
-//
-//   foo_callback.Run();  // Prints "1"
-//   foo_callback.Run();  // Prints "1"
-//   *n = 2;
-//   foo_callback.Run();  // Prints "2"
-//
-//   foo_callback.Reset();  // |pn| is deleted.  Also will happen when
-//                          // |foo_callback| goes out of scope.
-//
-// Without Owned(), someone would have to know to delete |pn| when the last
-// reference to the Callback is deleted.
-//
-//
-// EXAMPLE OF ConstRef():
-//
-//   void foo(int arg) { cout << arg << endl }
-//
-//   int n = 1;
-//   Closure no_ref = Bind(&foo, n);
-//   Closure has_ref = Bind(&foo, ConstRef(n));
-//
-//   no_ref.Run();  // Prints "1"
-//   has_ref.Run();  // Prints "1"
-//
-//   n = 2;
-//   no_ref.Run();  // Prints "1"
-//   has_ref.Run();  // Prints "2"
-//
-// Note that because ConstRef() takes a reference on |n|, |n| must outlive all
-// its bound callbacks.
-//
-//
-// EXAMPLE OF IgnoreResult():
-//
-//   int DoSomething(int arg) { cout << arg << endl; }
-//
-//   // Assign to a Callback with a void return type.
-//   Callback<void(int)> cb = Bind(IgnoreResult(&DoSomething));
-//   cb->Run(1);  // Prints "1".
-//
-//   // Prints "1" on |ml|.
-//   ml->PostTask(FROM_HERE, Bind(IgnoreResult(&DoSomething), 1);
-//
-//
-// EXAMPLE OF Passed():
-//
-//   void TakesOwnership(scoped_ptr<Foo> arg) { }
-//   scoped_ptr<Foo> CreateFoo() { return scoped_ptr<Foo>(new Foo()); }
-//
-//   scoped_ptr<Foo> f(new Foo());
-//
-//   // |cb| is given ownership of Foo(). |f| is now NULL.
-//   // You can use f.Pass() in place of &f, but it's more verbose.
-//   Closure cb = Bind(&TakesOwnership, Passed(&f));
-//
-//   // Run was never called so |cb| still owns Foo() and deletes
-//   // it on Reset().
-//   cb.Reset();
-//
-//   // |cb| is given a new Foo created by CreateFoo().
-//   cb = Bind(&TakesOwnership, Passed(CreateFoo()));
-//
-//   // |arg| in TakesOwnership() is given ownership of Foo(). |cb|
-//   // no longer owns Foo() and, if reset, would not delete Foo().
-//   cb.Run();  // Foo() is now transferred to |arg| and deleted.
-//   cb.Run();  // This CHECK()s since Foo() already been used once.
-//
-// Passed() is particularly useful with PostTask() when you are transferring
-// ownership of an argument into a task, but don't necessarily know if the
-// task will always be executed. This can happen if the task is cancellable
-// or if it is posted to a TaskRunner.
-//
-//
-// SIMPLE FUNCTIONS AND UTILITIES.
-//
-//   DoNothing() - Useful for creating a Closure that does nothing when called.
-//   DeletePointer<T>() - Useful for creating a Closure that will delete a
-//                        pointer when invoked. Only use this when necessary.
-//                        In most cases MessageLoop::DeleteSoon() is a better
-//                        fit.
-
-#ifndef BASE_BIND_HELPERS_H_
-#define BASE_BIND_HELPERS_H_
-
-#include "base/basictypes.h"
-#include "base/callback.h"
-#include "base/memory/weak_ptr.h"
-#include "base/template_util.h"
-
-namespace base {
-namespace internal {
-
-// Use the Substitution Failure Is Not An Error (SFINAE) trick to inspect T
-// for the existence of AddRef() and Release() functions of the correct
-// signature.
-//
-// http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error
-// http://stackoverflow.com/questions/257288/is-it-possible-to-write-a-c-template-to-check-for-a-functions-existence
-// http://stackoverflow.com/questions/4358584/sfinae-approach-comparison
-// http://stackoverflow.com/questions/1966362/sfinae-to-check-for-inherited-member-functions
-//
-// The last link in particular show the method used below.
-//
-// For SFINAE to work with inherited methods, we need to pull some extra tricks
-// with multiple inheritance.  In the more standard formulation, the overloads
-// of Check would be:
-//
-//   template <typename C>
-//   Yes NotTheCheckWeWant(Helper<&C::TargetFunc>*);
-//
-//   template <typename C>
-//   No NotTheCheckWeWant(...);
-//
-//   static const bool value = sizeof(NotTheCheckWeWant<T>(0)) == sizeof(Yes);
-//
-// The problem here is that template resolution will not match
-// C::TargetFunc if TargetFunc does not exist directly in C.  That is, if
-// TargetFunc in inherited from an ancestor, &C::TargetFunc will not match,
-// |value| will be false.  This formulation only checks for whether or
-// not TargetFunc exist directly in the class being introspected.
-//
-// To get around this, we play a dirty trick with multiple inheritance.
-// First, We create a class BaseMixin that declares each function that we
-// want to probe for.  Then we create a class Base that inherits from both T
-// (the class we wish to probe) and BaseMixin.  Note that the function
-// signature in BaseMixin does not need to match the signature of the function
-// we are probing for; thus it's easiest to just use void(void).
-//
-// Now, if TargetFunc exists somewhere in T, then &Base::TargetFunc has an
-// ambiguous resolution between BaseMixin and T.  This lets us write the
-// following:
-//
-//   template <typename C>
-//   No GoodCheck(Helper<&C::TargetFunc>*);
-//
-//   template <typename C>
-//   Yes GoodCheck(...);
-//
-//   static const bool value = sizeof(GoodCheck<Base>(0)) == sizeof(Yes);
-//
-// Notice here that the variadic version of GoodCheck() returns Yes here
-// instead of No like the previous one. Also notice that we calculate |value|
-// by specializing GoodCheck() on Base instead of T.
-//
-// We've reversed the roles of the variadic, and Helper overloads.
-// GoodCheck(Helper<&C::TargetFunc>*), when C = Base, fails to be a valid
-// substitution if T::TargetFunc exists. Thus GoodCheck<Base>(0) will resolve
-// to the variadic version if T has TargetFunc.  If T::TargetFunc does not
-// exist, then &C::TargetFunc is not ambiguous, and the overload resolution
-// will prefer GoodCheck(Helper<&C::TargetFunc>*).
-//
-// This method of SFINAE will correctly probe for inherited names, but it cannot
-// typecheck those names.  It's still a good enough sanity check though.
-//
-// Works on gcc-4.2, gcc-4.4, and Visual Studio 2008.
-//
-// TODO(ajwong): Move to ref_counted.h or template_util.h when we've vetted
-// this works well.
-//
-// TODO(ajwong): Make this check for Release() as well.
-// See http://crbug.com/82038.
-template <typename T>
-class SupportsAddRefAndRelease {
-  typedef char Yes[1];
-  typedef char No[2];
-
-  struct BaseMixin {
-    void AddRef();
-  };
-
-// MSVC warns when you try to use Base if T has a private destructor, the
-// common pattern for refcounted types. It does this even though no attempt to
-// instantiate Base is made.  We disable the warning for this definition.
-#if defined(OS_WIN)
-#pragma warning(push)
-#pragma warning(disable:4624)
-#endif
-  struct Base : public T, public BaseMixin {
-  };
-#if defined(OS_WIN)
-#pragma warning(pop)
-#endif
-
-  template <void(BaseMixin::*)(void)> struct Helper {};
-
-  template <typename C>
-  static No& Check(Helper<&C::AddRef>*);
-
-  template <typename >
-  static Yes& Check(...);
-
- public:
-  enum { value = sizeof(Check<Base>(0)) == sizeof(Yes) };
-};
-
-// Helpers to assert that arguments of a recounted type are bound with a
-// scoped_refptr.
-template <bool IsClasstype, typename T>
-struct UnsafeBindtoRefCountedArgHelper : false_type {
-};
-
-template <typename T>
-struct UnsafeBindtoRefCountedArgHelper<true, T>
-    : integral_constant<bool, SupportsAddRefAndRelease<T>::value> {
-};
-
-template <typename T>
-struct UnsafeBindtoRefCountedArg : false_type {
-};
-
-template <typename T>
-struct UnsafeBindtoRefCountedArg<T*>
-    : UnsafeBindtoRefCountedArgHelper<is_class<T>::value, T> {
-};
-
-template <typename T>
-class HasIsMethodTag {
-  typedef char Yes[1];
-  typedef char No[2];
-
-  template <typename U>
-  static Yes& Check(typename U::IsMethod*);
-
-  template <typename U>
-  static No& Check(...);
-
- public:
-  enum { value = sizeof(Check<T>(0)) == sizeof(Yes) };
-};
-
-template <typename T>
-class UnretainedWrapper {
- public:
-  explicit UnretainedWrapper(T* o) : ptr_(o) {}
-  T* get() const { return ptr_; }
- private:
-  T* ptr_;
-};
-
-template <typename T>
-class ConstRefWrapper {
- public:
-  explicit ConstRefWrapper(const T& o) : ptr_(&o) {}
-  const T& get() const { return *ptr_; }
- private:
-  const T* ptr_;
-};
-
-template <typename T>
-struct IgnoreResultHelper {
-  explicit IgnoreResultHelper(T functor) : functor_(functor) {}
-
-  T functor_;
-};
-
-template <typename T>
-struct IgnoreResultHelper<Callback<T> > {
-  explicit IgnoreResultHelper(const Callback<T>& functor) : functor_(functor) {}
-
-  const Callback<T>& functor_;
-};
-
-// An alternate implementation is to avoid the destructive copy, and instead
-// specialize ParamTraits<> for OwnedWrapper<> to change the StorageType to
-// a class that is essentially a scoped_ptr<>.
-//
-// The current implementation has the benefit though of leaving ParamTraits<>
-// fully in callback_internal.h as well as avoiding type conversions during
-// storage.
-template <typename T>
-class OwnedWrapper {
- public:
-  explicit OwnedWrapper(T* o) : ptr_(o) {}
-  ~OwnedWrapper() { delete ptr_; }
-  T* get() const { return ptr_; }
-  OwnedWrapper(const OwnedWrapper& other) {
-    ptr_ = other.ptr_;
-    other.ptr_ = NULL;
-  }
-
- private:
-  mutable T* ptr_;
-};
-
-// PassedWrapper is a copyable adapter for a scoper that ignores const.
-//
-// It is needed to get around the fact that Bind() takes a const reference to
-// all its arguments.  Because Bind() takes a const reference to avoid
-// unnecessary copies, it is incompatible with movable-but-not-copyable
-// types; doing a destructive "move" of the type into Bind() would violate
-// the const correctness.
-//
-// This conundrum cannot be solved without either C++11 rvalue references or
-// a O(2^n) blowup of Bind() templates to handle each combination of regular
-// types and movable-but-not-copyable types.  Thus we introduce a wrapper type
-// that is copyable to transmit the correct type information down into
-// BindState<>. Ignoring const in this type makes sense because it is only
-// created when we are explicitly trying to do a destructive move.
-//
-// Two notes:
-//  1) PassedWrapper supports any type that has a "Pass()" function.
-//     This is intentional. The whitelisting of which specific types we
-//     support is maintained by CallbackParamTraits<>.
-//  2) is_valid_ is distinct from NULL because it is valid to bind a "NULL"
-//     scoper to a Callback and allow the Callback to execute once.
-template <typename T>
-class PassedWrapper {
- public:
-  explicit PassedWrapper(T scoper) : is_valid_(true), scoper_(scoper.Pass()) {}
-  PassedWrapper(const PassedWrapper& other)
-      : is_valid_(other.is_valid_), scoper_(other.scoper_.Pass()) {
-  }
-  T Pass() const {
-    CHECK(is_valid_);
-    is_valid_ = false;
-    return scoper_.Pass();
-  }
-
- private:
-  mutable bool is_valid_;
-  mutable T scoper_;
-};
-
-// Unwrap the stored parameters for the wrappers above.
-template <typename T>
-struct UnwrapTraits {
-  typedef const T& ForwardType;
-  static ForwardType Unwrap(const T& o) { return o; }
-};
-
-template <typename T>
-struct UnwrapTraits<UnretainedWrapper<T> > {
-  typedef T* ForwardType;
-  static ForwardType Unwrap(UnretainedWrapper<T> unretained) {
-    return unretained.get();
-  }
-};
-
-template <typename T>
-struct UnwrapTraits<ConstRefWrapper<T> > {
-  typedef const T& ForwardType;
-  static ForwardType Unwrap(ConstRefWrapper<T> const_ref) {
-    return const_ref.get();
-  }
-};
-
-template <typename T>
-struct UnwrapTraits<scoped_refptr<T> > {
-  typedef T* ForwardType;
-  static ForwardType Unwrap(const scoped_refptr<T>& o) { return o.get(); }
-};
-
-template <typename T>
-struct UnwrapTraits<WeakPtr<T> > {
-  typedef const WeakPtr<T>& ForwardType;
-  static ForwardType Unwrap(const WeakPtr<T>& o) { return o; }
-};
-
-template <typename T>
-struct UnwrapTraits<OwnedWrapper<T> > {
-  typedef T* ForwardType;
-  static ForwardType Unwrap(const OwnedWrapper<T>& o) {
-    return o.get();
-  }
-};
-
-template <typename T>
-struct UnwrapTraits<PassedWrapper<T> > {
-  typedef T ForwardType;
-  static T Unwrap(PassedWrapper<T>& o) {
-    return o.Pass();
-  }
-};
-
-// Utility for handling different refcounting semantics in the Bind()
-// function.
-template <bool is_method, typename... T>
-struct MaybeScopedRefPtr;
-
-template <bool is_method>
-struct MaybeScopedRefPtr<is_method> {
-  MaybeScopedRefPtr() {}
-};
-
-template <typename T, typename... Rest>
-struct MaybeScopedRefPtr<false, T, Rest...> {
-  MaybeScopedRefPtr(const T&, const Rest&...) {}
-};
-
-template <typename T, size_t n, typename... Rest>
-struct MaybeScopedRefPtr<false, T[n], Rest...> {
-  MaybeScopedRefPtr(const T*, const Rest&...) {}
-};
-
-template <typename T, typename... Rest>
-struct MaybeScopedRefPtr<true, T, Rest...> {
-  MaybeScopedRefPtr(const T& o, const Rest&...) {}
-};
-
-template <typename T, typename... Rest>
-struct MaybeScopedRefPtr<true, T*, Rest...> {
-  MaybeScopedRefPtr(T* o, const Rest&...) : ref_(o) {}
-  scoped_refptr<T> ref_;
-};
-
-// No need to additionally AddRef() and Release() since we are storing a
-// scoped_refptr<> inside the storage object already.
-template <typename T, typename... Rest>
-struct MaybeScopedRefPtr<true, scoped_refptr<T>, Rest...> {
-  MaybeScopedRefPtr(const scoped_refptr<T>&, const Rest&...) {}
-};
-
-template <typename T, typename... Rest>
-struct MaybeScopedRefPtr<true, const T*, Rest...> {
-  MaybeScopedRefPtr(const T* o, const Rest&...) : ref_(o) {}
-  scoped_refptr<const T> ref_;
-};
-
-// IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a
-// method.  It is used internally by Bind() to select the correct
-// InvokeHelper that will no-op itself in the event the WeakPtr<> for
-// the target object is invalidated.
-//
-// The first argument should be the type of the object that will be received by
-// the method.
-template <bool IsMethod, typename... Args>
-struct IsWeakMethod : public false_type {};
-
-template <typename T, typename... Args>
-struct IsWeakMethod<true, WeakPtr<T>, Args...> : public true_type {};
-
-template <typename T, typename... Args>
-struct IsWeakMethod<true, ConstRefWrapper<WeakPtr<T>>, Args...>
-    : public true_type {};
-
-
-// Packs a list of types to hold them in a single type.
-template <typename... Types>
-struct TypeList {};
-
-// Used for DropTypeListItem implementation.
-template <size_t n, typename List>
-struct DropTypeListItemImpl;
-
-// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure.
-template <size_t n, typename T, typename... List>
-struct DropTypeListItemImpl<n, TypeList<T, List...>>
-    : DropTypeListItemImpl<n - 1, TypeList<List...>> {};
-
-template <typename T, typename... List>
-struct DropTypeListItemImpl<0, TypeList<T, List...>> {
-  typedef TypeList<T, List...> Type;
-};
-
-template <>
-struct DropTypeListItemImpl<0, TypeList<>> {
-  typedef TypeList<> Type;
-};
-
-// A type-level function that drops |n| list item from given TypeList.
-template <size_t n, typename List>
-using DropTypeListItem = typename DropTypeListItemImpl<n, List>::Type;
-
-// Used for ConcatTypeLists implementation.
-template <typename List1, typename List2>
-struct ConcatTypeListsImpl;
-
-template <typename... Types1, typename... Types2>
-struct ConcatTypeListsImpl<TypeList<Types1...>, TypeList<Types2...>> {
-  typedef TypeList<Types1..., Types2...> Type;
-};
-
-// A type-level function that concats two TypeLists.
-template <typename List1, typename List2>
-using ConcatTypeLists = typename ConcatTypeListsImpl<List1, List2>::Type;
-
-// Used for MakeFunctionType implementation.
-template <typename R, typename ArgList>
-struct MakeFunctionTypeImpl;
-
-template <typename R, typename... Args>
-struct MakeFunctionTypeImpl<R, TypeList<Args...>> {
-  typedef R(Type)(Args...);
-};
-
-// A type-level function that constructs a function type that has |R| as its
-// return type and has TypeLists items as its arguments.
-template <typename R, typename ArgList>
-using MakeFunctionType = typename MakeFunctionTypeImpl<R, ArgList>::Type;
-
-}  // namespace internal
-
-template <typename T>
-static inline internal::UnretainedWrapper<T> Unretained(T* o) {
-  return internal::UnretainedWrapper<T>(o);
-}
-
-template <typename T>
-static inline internal::ConstRefWrapper<T> ConstRef(const T& o) {
-  return internal::ConstRefWrapper<T>(o);
-}
-
-template <typename T>
-static inline internal::OwnedWrapper<T> Owned(T* o) {
-  return internal::OwnedWrapper<T>(o);
-}
-
-// We offer 2 syntaxes for calling Passed().  The first takes a temporary and
-// is best suited for use with the return value of a function. The second
-// takes a pointer to the scoper and is just syntactic sugar to avoid having
-// to write Passed(scoper.Pass()).
-template <typename T>
-static inline internal::PassedWrapper<T> Passed(T scoper) {
-  return internal::PassedWrapper<T>(scoper.Pass());
-}
-template <typename T>
-static inline internal::PassedWrapper<T> Passed(T* scoper) {
-  return internal::PassedWrapper<T>(scoper->Pass());
-}
-
-template <typename T>
-static inline internal::IgnoreResultHelper<T> IgnoreResult(T data) {
-  return internal::IgnoreResultHelper<T>(data);
-}
-
-template <typename T>
-static inline internal::IgnoreResultHelper<Callback<T> >
-IgnoreResult(const Callback<T>& data) {
-  return internal::IgnoreResultHelper<Callback<T> >(data);
-}
-
-BASE_EXPORT void DoNothing();
-
-template<typename T>
-void DeletePointer(T* obj) {
-  delete obj;
-}
-
-}  // namespace base
-
-#endif  // BASE_BIND_HELPERS_H_