1// Copyright (c) 2011 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5// This defines a set of argument wrappers and related factory methods that 6// can be used specify the refcounting and reference semantics of arguments 7// that are bound by the Bind() function in base/bind.h. 8// 9// It also defines a set of simple functions and utilities that people want 10// when using Callback<> and Bind(). 11// 12// 13// ARGUMENT BINDING WRAPPERS 14// 15// The wrapper functions are base::Unretained(), base::Owned(), base::Passed(), 16// base::ConstRef(), and base::IgnoreResult(). 17// 18// Unretained() allows Bind() to bind a non-refcounted class, and to disable 19// refcounting on arguments that are refcounted objects. 20// 21// Owned() transfers ownership of an object to the Callback resulting from 22// bind; the object will be deleted when the Callback is deleted. 23// 24// Passed() is for transferring movable-but-not-copyable types (eg. scoped_ptr) 25// through a Callback. Logically, this signifies a destructive transfer of 26// the state of the argument into the target function. Invoking 27// Callback::Run() twice on a Callback that was created with a Passed() 28// argument will CHECK() because the first invocation would have already 29// transferred ownership to the target function. 30// 31// ConstRef() allows binding a constant reference to an argument rather 32// than a copy. 33// 34// IgnoreResult() is used to adapt a function or Callback with a return type to 35// one with a void return. This is most useful if you have a function with, 36// say, a pesky ignorable bool return that you want to use with PostTask or 37// something else that expect a Callback with a void return. 38// 39// EXAMPLE OF Unretained(): 40// 41// class Foo { 42// public: 43// void func() { cout << "Foo:f" << endl; } 44// }; 45// 46// // In some function somewhere. 47// Foo foo; 48// Closure foo_callback = 49// Bind(&Foo::func, Unretained(&foo)); 50// foo_callback.Run(); // Prints "Foo:f". 51// 52// Without the Unretained() wrapper on |&foo|, the above call would fail 53// to compile because Foo does not support the AddRef() and Release() methods. 54// 55// 56// EXAMPLE OF Owned(): 57// 58// void foo(int* arg) { cout << *arg << endl } 59// 60// int* pn = new int(1); 61// Closure foo_callback = Bind(&foo, Owned(pn)); 62// 63// foo_callback.Run(); // Prints "1" 64// foo_callback.Run(); // Prints "1" 65// *n = 2; 66// foo_callback.Run(); // Prints "2" 67// 68// foo_callback.Reset(); // |pn| is deleted. Also will happen when 69// // |foo_callback| goes out of scope. 70// 71// Without Owned(), someone would have to know to delete |pn| when the last 72// reference to the Callback is deleted. 73// 74// 75// EXAMPLE OF ConstRef(): 76// 77// void foo(int arg) { cout << arg << endl } 78// 79// int n = 1; 80// Closure no_ref = Bind(&foo, n); 81// Closure has_ref = Bind(&foo, ConstRef(n)); 82// 83// no_ref.Run(); // Prints "1" 84// has_ref.Run(); // Prints "1" 85// 86// n = 2; 87// no_ref.Run(); // Prints "1" 88// has_ref.Run(); // Prints "2" 89// 90// Note that because ConstRef() takes a reference on |n|, |n| must outlive all 91// its bound callbacks. 92// 93// 94// EXAMPLE OF IgnoreResult(): 95// 96// int DoSomething(int arg) { cout << arg << endl; } 97// 98// // Assign to a Callback with a void return type. 99// Callback<void(int)> cb = Bind(IgnoreResult(&DoSomething)); 100// cb->Run(1); // Prints "1". 101// 102// // Prints "1" on |ml|. 103// ml->PostTask(FROM_HERE, Bind(IgnoreResult(&DoSomething), 1); 104// 105// 106// EXAMPLE OF Passed(): 107// 108// void TakesOwnership(scoped_ptr<Foo> arg) { } 109// scoped_ptr<Foo> CreateFoo() { return scoped_ptr<Foo>(new Foo()); } 110// 111// scoped_ptr<Foo> f(new Foo()); 112// 113// // |cb| is given ownership of Foo(). |f| is now NULL. 114// // You can use std::move(f) in place of &f, but it's more verbose. 115// Closure cb = Bind(&TakesOwnership, Passed(&f)); 116// 117// // Run was never called so |cb| still owns Foo() and deletes 118// // it on Reset(). 119// cb.Reset(); 120// 121// // |cb| is given a new Foo created by CreateFoo(). 122// cb = Bind(&TakesOwnership, Passed(CreateFoo())); 123// 124// // |arg| in TakesOwnership() is given ownership of Foo(). |cb| 125// // no longer owns Foo() and, if reset, would not delete Foo(). 126// cb.Run(); // Foo() is now transferred to |arg| and deleted. 127// cb.Run(); // This CHECK()s since Foo() already been used once. 128// 129// Passed() is particularly useful with PostTask() when you are transferring 130// ownership of an argument into a task, but don't necessarily know if the 131// task will always be executed. This can happen if the task is cancellable 132// or if it is posted to a TaskRunner. 133// 134// 135// SIMPLE FUNCTIONS AND UTILITIES. 136// 137// DoNothing() - Useful for creating a Closure that does nothing when called. 138// DeletePointer<T>() - Useful for creating a Closure that will delete a 139// pointer when invoked. Only use this when necessary. 140// In most cases MessageLoop::DeleteSoon() is a better 141// fit. 142 143#ifndef BASE_BIND_HELPERS_H_ 144#define BASE_BIND_HELPERS_H_ 145 146#include <stddef.h> 147 148#include <map> 149#include <memory> 150#include <type_traits> 151#include <utility> 152#include <vector> 153 154#include "base/callback.h" 155#include "base/memory/weak_ptr.h" 156#include "base/template_util.h" 157#include "build/build_config.h" 158 159namespace base { 160namespace internal { 161 162// Use the Substitution Failure Is Not An Error (SFINAE) trick to inspect T 163// for the existence of AddRef() and Release() functions of the correct 164// signature. 165// 166// http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error 167// http://stackoverflow.com/questions/257288/is-it-possible-to-write-a-c-template-to-check-for-a-functions-existence 168// http://stackoverflow.com/questions/4358584/sfinae-approach-comparison 169// http://stackoverflow.com/questions/1966362/sfinae-to-check-for-inherited-member-functions 170// 171// The last link in particular show the method used below. 172// 173// For SFINAE to work with inherited methods, we need to pull some extra tricks 174// with multiple inheritance. In the more standard formulation, the overloads 175// of Check would be: 176// 177// template <typename C> 178// Yes NotTheCheckWeWant(Helper<&C::TargetFunc>*); 179// 180// template <typename C> 181// No NotTheCheckWeWant(...); 182// 183// static const bool value = sizeof(NotTheCheckWeWant<T>(0)) == sizeof(Yes); 184// 185// The problem here is that template resolution will not match 186// C::TargetFunc if TargetFunc does not exist directly in C. That is, if 187// TargetFunc in inherited from an ancestor, &C::TargetFunc will not match, 188// |value| will be false. This formulation only checks for whether or 189// not TargetFunc exist directly in the class being introspected. 190// 191// To get around this, we play a dirty trick with multiple inheritance. 192// First, We create a class BaseMixin that declares each function that we 193// want to probe for. Then we create a class Base that inherits from both T 194// (the class we wish to probe) and BaseMixin. Note that the function 195// signature in BaseMixin does not need to match the signature of the function 196// we are probing for; thus it's easiest to just use void(). 197// 198// Now, if TargetFunc exists somewhere in T, then &Base::TargetFunc has an 199// ambiguous resolution between BaseMixin and T. This lets us write the 200// following: 201// 202// template <typename C> 203// No GoodCheck(Helper<&C::TargetFunc>*); 204// 205// template <typename C> 206// Yes GoodCheck(...); 207// 208// static const bool value = sizeof(GoodCheck<Base>(0)) == sizeof(Yes); 209// 210// Notice here that the variadic version of GoodCheck() returns Yes here 211// instead of No like the previous one. Also notice that we calculate |value| 212// by specializing GoodCheck() on Base instead of T. 213// 214// We've reversed the roles of the variadic, and Helper overloads. 215// GoodCheck(Helper<&C::TargetFunc>*), when C = Base, fails to be a valid 216// substitution if T::TargetFunc exists. Thus GoodCheck<Base>(0) will resolve 217// to the variadic version if T has TargetFunc. If T::TargetFunc does not 218// exist, then &C::TargetFunc is not ambiguous, and the overload resolution 219// will prefer GoodCheck(Helper<&C::TargetFunc>*). 220// 221// This method of SFINAE will correctly probe for inherited names, but it cannot 222// typecheck those names. It's still a good enough sanity check though. 223// 224// Works on gcc-4.2, gcc-4.4, and Visual Studio 2008. 225// 226// TODO(ajwong): Move to ref_counted.h or template_util.h when we've vetted 227// this works well. 228// 229// TODO(ajwong): Make this check for Release() as well. 230// See http://crbug.com/82038. 231template <typename T> 232class SupportsAddRefAndRelease { 233 using Yes = char[1]; 234 using No = char[2]; 235 236 struct BaseMixin { 237 void AddRef(); 238 }; 239 240// MSVC warns when you try to use Base if T has a private destructor, the 241// common pattern for refcounted types. It does this even though no attempt to 242// instantiate Base is made. We disable the warning for this definition. 243#if defined(OS_WIN) 244#pragma warning(push) 245#pragma warning(disable:4624) 246#endif 247 struct Base : public T, public BaseMixin { 248 }; 249#if defined(OS_WIN) 250#pragma warning(pop) 251#endif 252 253 template <void(BaseMixin::*)()> struct Helper {}; 254 255 template <typename C> 256 static No& Check(Helper<&C::AddRef>*); 257 258 template <typename > 259 static Yes& Check(...); 260 261 public: 262 enum { value = sizeof(Check<Base>(0)) == sizeof(Yes) }; 263}; 264 265// Helpers to assert that arguments of a recounted type are bound with a 266// scoped_refptr. 267template <bool IsClasstype, typename T> 268struct UnsafeBindtoRefCountedArgHelper : false_type { 269}; 270 271template <typename T> 272struct UnsafeBindtoRefCountedArgHelper<true, T> 273 : integral_constant<bool, SupportsAddRefAndRelease<T>::value> { 274}; 275 276template <typename T> 277struct UnsafeBindtoRefCountedArg : false_type { 278}; 279 280template <typename T> 281struct UnsafeBindtoRefCountedArg<T*> 282 : UnsafeBindtoRefCountedArgHelper<is_class<T>::value, T> { 283}; 284 285template <typename T> 286class HasIsMethodTag { 287 using Yes = char[1]; 288 using No = char[2]; 289 290 template <typename U> 291 static Yes& Check(typename U::IsMethod*); 292 293 template <typename U> 294 static No& Check(...); 295 296 public: 297 enum { value = sizeof(Check<T>(0)) == sizeof(Yes) }; 298}; 299 300template <typename T> 301class UnretainedWrapper { 302 public: 303 explicit UnretainedWrapper(T* o) : ptr_(o) {} 304 T* get() const { return ptr_; } 305 private: 306 T* ptr_; 307}; 308 309template <typename T> 310class ConstRefWrapper { 311 public: 312 explicit ConstRefWrapper(const T& o) : ptr_(&o) {} 313 const T& get() const { return *ptr_; } 314 private: 315 const T* ptr_; 316}; 317 318template <typename T> 319struct IgnoreResultHelper { 320 explicit IgnoreResultHelper(T functor) : functor_(functor) {} 321 322 T functor_; 323}; 324 325template <typename T> 326struct IgnoreResultHelper<Callback<T> > { 327 explicit IgnoreResultHelper(const Callback<T>& functor) : functor_(functor) {} 328 329 const Callback<T>& functor_; 330}; 331 332// An alternate implementation is to avoid the destructive copy, and instead 333// specialize ParamTraits<> for OwnedWrapper<> to change the StorageType to 334// a class that is essentially a scoped_ptr<>. 335// 336// The current implementation has the benefit though of leaving ParamTraits<> 337// fully in callback_internal.h as well as avoiding type conversions during 338// storage. 339template <typename T> 340class OwnedWrapper { 341 public: 342 explicit OwnedWrapper(T* o) : ptr_(o) {} 343 ~OwnedWrapper() { delete ptr_; } 344 T* get() const { return ptr_; } 345 OwnedWrapper(const OwnedWrapper& other) { 346 ptr_ = other.ptr_; 347 other.ptr_ = NULL; 348 } 349 350 private: 351 mutable T* ptr_; 352}; 353 354// PassedWrapper is a copyable adapter for a scoper that ignores const. 355// 356// It is needed to get around the fact that Bind() takes a const reference to 357// all its arguments. Because Bind() takes a const reference to avoid 358// unnecessary copies, it is incompatible with movable-but-not-copyable 359// types; doing a destructive "move" of the type into Bind() would violate 360// the const correctness. 361// 362// This conundrum cannot be solved without either C++11 rvalue references or 363// a O(2^n) blowup of Bind() templates to handle each combination of regular 364// types and movable-but-not-copyable types. Thus we introduce a wrapper type 365// that is copyable to transmit the correct type information down into 366// BindState<>. Ignoring const in this type makes sense because it is only 367// created when we are explicitly trying to do a destructive move. 368// 369// Two notes: 370// 1) PassedWrapper supports any type that has a move constructor, however 371// the type will need to be specifically whitelisted in order for it to be 372// bound to a Callback. We guard this explicitly at the call of Passed() 373// to make for clear errors. Things not given to Passed() will be forwarded 374// and stored by value which will not work for general move-only types. 375// 2) is_valid_ is distinct from NULL because it is valid to bind a "NULL" 376// scoper to a Callback and allow the Callback to execute once. 377template <typename T> 378class PassedWrapper { 379 public: 380 explicit PassedWrapper(T&& scoper) 381 : is_valid_(true), scoper_(std::move(scoper)) {} 382 PassedWrapper(const PassedWrapper& other) 383 : is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {} 384 T Pass() const { 385 CHECK(is_valid_); 386 is_valid_ = false; 387 return std::move(scoper_); 388 } 389 390 private: 391 mutable bool is_valid_; 392 mutable T scoper_; 393}; 394 395// Specialize PassedWrapper for std::unique_ptr used by base::Passed(). 396// Use std::move() to transfer the data from one storage to another. 397template <typename T, typename D> 398class PassedWrapper<std::unique_ptr<T, D>> { 399 public: 400 explicit PassedWrapper(std::unique_ptr<T, D> scoper) 401 : is_valid_(true), scoper_(std::move(scoper)) {} 402 PassedWrapper(const PassedWrapper& other) 403 : is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {} 404 405 std::unique_ptr<T, D> Pass() const { 406 CHECK(is_valid_); 407 is_valid_ = false; 408 return std::move(scoper_); 409 } 410 411 private: 412 mutable bool is_valid_; 413 mutable std::unique_ptr<T, D> scoper_; 414}; 415 416// Specialize PassedWrapper for std::vector<std::unique_ptr<T>>. 417template <typename T, typename D, typename A> 418class PassedWrapper<std::vector<std::unique_ptr<T, D>, A>> { 419 public: 420 explicit PassedWrapper(std::vector<std::unique_ptr<T, D>, A> scoper) 421 : is_valid_(true), scoper_(std::move(scoper)) {} 422 PassedWrapper(const PassedWrapper& other) 423 : is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {} 424 425 std::vector<std::unique_ptr<T, D>, A> Pass() const { 426 CHECK(is_valid_); 427 is_valid_ = false; 428 return std::move(scoper_); 429 } 430 431 private: 432 mutable bool is_valid_; 433 mutable std::vector<std::unique_ptr<T, D>, A> scoper_; 434}; 435 436// Specialize PassedWrapper for std::map<K, std::unique_ptr<T>>. 437template <typename K, typename T, typename D, typename C, typename A> 438class PassedWrapper<std::map<K, std::unique_ptr<T, D>, C, A>> { 439 public: 440 explicit PassedWrapper(std::map<K, std::unique_ptr<T, D>, C, A> scoper) 441 : is_valid_(true), scoper_(std::move(scoper)) {} 442 PassedWrapper(const PassedWrapper& other) 443 : is_valid_(other.is_valid_), scoper_(std::move(other.scoper_)) {} 444 445 std::map<K, std::unique_ptr<T, D>, C, A> Pass() const { 446 CHECK(is_valid_); 447 is_valid_ = false; 448 return std::move(scoper_); 449 } 450 451 private: 452 mutable bool is_valid_; 453 mutable std::map<K, std::unique_ptr<T, D>, C, A> scoper_; 454}; 455 456// Unwrap the stored parameters for the wrappers above. 457template <typename T> 458struct UnwrapTraits { 459 using ForwardType = const T&; 460 static ForwardType Unwrap(const T& o) { return o; } 461}; 462 463template <typename T> 464struct UnwrapTraits<UnretainedWrapper<T> > { 465 using ForwardType = T*; 466 static ForwardType Unwrap(UnretainedWrapper<T> unretained) { 467 return unretained.get(); 468 } 469}; 470 471template <typename T> 472struct UnwrapTraits<ConstRefWrapper<T> > { 473 using ForwardType = const T&; 474 static ForwardType Unwrap(ConstRefWrapper<T> const_ref) { 475 return const_ref.get(); 476 } 477}; 478 479template <typename T> 480struct UnwrapTraits<scoped_refptr<T> > { 481 using ForwardType = T*; 482 static ForwardType Unwrap(const scoped_refptr<T>& o) { return o.get(); } 483}; 484 485template <typename T> 486struct UnwrapTraits<WeakPtr<T> > { 487 using ForwardType = const WeakPtr<T>&; 488 static ForwardType Unwrap(const WeakPtr<T>& o) { return o; } 489}; 490 491template <typename T> 492struct UnwrapTraits<OwnedWrapper<T> > { 493 using ForwardType = T*; 494 static ForwardType Unwrap(const OwnedWrapper<T>& o) { 495 return o.get(); 496 } 497}; 498 499template <typename T> 500struct UnwrapTraits<PassedWrapper<T> > { 501 using ForwardType = T; 502 static T Unwrap(PassedWrapper<T>& o) { 503 return o.Pass(); 504 } 505}; 506 507// Utility for handling different refcounting semantics in the Bind() 508// function. 509template <bool is_method, typename... T> 510struct MaybeScopedRefPtr; 511 512template <bool is_method> 513struct MaybeScopedRefPtr<is_method> { 514 MaybeScopedRefPtr() {} 515}; 516 517template <typename T, typename... Rest> 518struct MaybeScopedRefPtr<false, T, Rest...> { 519 MaybeScopedRefPtr(const T&, const Rest&...) {} 520}; 521 522template <typename T, size_t n, typename... Rest> 523struct MaybeScopedRefPtr<false, T[n], Rest...> { 524 MaybeScopedRefPtr(const T*, const Rest&...) {} 525}; 526 527template <typename T, typename... Rest> 528struct MaybeScopedRefPtr<true, T, Rest...> { 529 MaybeScopedRefPtr(const T& /* o */, const Rest&...) {} 530}; 531 532template <typename T, typename... Rest> 533struct MaybeScopedRefPtr<true, T*, Rest...> { 534 MaybeScopedRefPtr(T* o, const Rest&...) : ref_(o) {} 535 scoped_refptr<T> ref_; 536}; 537 538// No need to additionally AddRef() and Release() since we are storing a 539// scoped_refptr<> inside the storage object already. 540template <typename T, typename... Rest> 541struct MaybeScopedRefPtr<true, scoped_refptr<T>, Rest...> { 542 MaybeScopedRefPtr(const scoped_refptr<T>&, const Rest&...) {} 543}; 544 545template <typename T, typename... Rest> 546struct MaybeScopedRefPtr<true, const T*, Rest...> { 547 MaybeScopedRefPtr(const T* o, const Rest&...) : ref_(o) {} 548 scoped_refptr<const T> ref_; 549}; 550 551// IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a 552// method. It is used internally by Bind() to select the correct 553// InvokeHelper that will no-op itself in the event the WeakPtr<> for 554// the target object is invalidated. 555// 556// The first argument should be the type of the object that will be received by 557// the method. 558template <bool IsMethod, typename... Args> 559struct IsWeakMethod : public false_type {}; 560 561template <typename T, typename... Args> 562struct IsWeakMethod<true, WeakPtr<T>, Args...> : public true_type {}; 563 564template <typename T, typename... Args> 565struct IsWeakMethod<true, ConstRefWrapper<WeakPtr<T>>, Args...> 566 : public true_type {}; 567 568 569// Packs a list of types to hold them in a single type. 570template <typename... Types> 571struct TypeList {}; 572 573// Used for DropTypeListItem implementation. 574template <size_t n, typename List> 575struct DropTypeListItemImpl; 576 577// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure. 578template <size_t n, typename T, typename... List> 579struct DropTypeListItemImpl<n, TypeList<T, List...>> 580 : DropTypeListItemImpl<n - 1, TypeList<List...>> {}; 581 582template <typename T, typename... List> 583struct DropTypeListItemImpl<0, TypeList<T, List...>> { 584 using Type = TypeList<T, List...>; 585}; 586 587template <> 588struct DropTypeListItemImpl<0, TypeList<>> { 589 using Type = TypeList<>; 590}; 591 592// A type-level function that drops |n| list item from given TypeList. 593template <size_t n, typename List> 594using DropTypeListItem = typename DropTypeListItemImpl<n, List>::Type; 595 596// Used for TakeTypeListItem implementation. 597template <size_t n, typename List, typename... Accum> 598struct TakeTypeListItemImpl; 599 600// Do not use enable_if and SFINAE here to avoid MSVC2013 compile failure. 601template <size_t n, typename T, typename... List, typename... Accum> 602struct TakeTypeListItemImpl<n, TypeList<T, List...>, Accum...> 603 : TakeTypeListItemImpl<n - 1, TypeList<List...>, Accum..., T> {}; 604 605template <typename T, typename... List, typename... Accum> 606struct TakeTypeListItemImpl<0, TypeList<T, List...>, Accum...> { 607 using Type = TypeList<Accum...>; 608}; 609 610template <typename... Accum> 611struct TakeTypeListItemImpl<0, TypeList<>, Accum...> { 612 using Type = TypeList<Accum...>; 613}; 614 615// A type-level function that takes first |n| list item from given TypeList. 616// E.g. TakeTypeListItem<3, TypeList<A, B, C, D>> is evaluated to 617// TypeList<A, B, C>. 618template <size_t n, typename List> 619using TakeTypeListItem = typename TakeTypeListItemImpl<n, List>::Type; 620 621// Used for ConcatTypeLists implementation. 622template <typename List1, typename List2> 623struct ConcatTypeListsImpl; 624 625template <typename... Types1, typename... Types2> 626struct ConcatTypeListsImpl<TypeList<Types1...>, TypeList<Types2...>> { 627 using Type = TypeList<Types1..., Types2...>; 628}; 629 630// A type-level function that concats two TypeLists. 631template <typename List1, typename List2> 632using ConcatTypeLists = typename ConcatTypeListsImpl<List1, List2>::Type; 633 634// Used for MakeFunctionType implementation. 635template <typename R, typename ArgList> 636struct MakeFunctionTypeImpl; 637 638template <typename R, typename... Args> 639struct MakeFunctionTypeImpl<R, TypeList<Args...>> { 640 // MSVC 2013 doesn't support Type Alias of function types. 641 // Revisit this after we update it to newer version. 642 typedef R Type(Args...); 643}; 644 645// A type-level function that constructs a function type that has |R| as its 646// return type and has TypeLists items as its arguments. 647template <typename R, typename ArgList> 648using MakeFunctionType = typename MakeFunctionTypeImpl<R, ArgList>::Type; 649 650// Used for ExtractArgs. 651template <typename Signature> 652struct ExtractArgsImpl; 653 654template <typename R, typename... Args> 655struct ExtractArgsImpl<R(Args...)> { 656 using Type = TypeList<Args...>; 657}; 658 659// A type-level function that extracts function arguments into a TypeList. 660// E.g. ExtractArgs<R(A, B, C)> is evaluated to TypeList<A, B, C>. 661template <typename Signature> 662using ExtractArgs = typename ExtractArgsImpl<Signature>::Type; 663 664} // namespace internal 665 666template <typename T> 667static inline internal::UnretainedWrapper<T> Unretained(T* o) { 668 return internal::UnretainedWrapper<T>(o); 669} 670 671template <typename T> 672static inline internal::ConstRefWrapper<T> ConstRef(const T& o) { 673 return internal::ConstRefWrapper<T>(o); 674} 675 676template <typename T> 677static inline internal::OwnedWrapper<T> Owned(T* o) { 678 return internal::OwnedWrapper<T>(o); 679} 680 681// We offer 2 syntaxes for calling Passed(). The first takes an rvalue and 682// is best suited for use with the return value of a function or other temporary 683// rvalues. The second takes a pointer to the scoper and is just syntactic sugar 684// to avoid having to write Passed(std::move(scoper)). 685// 686// Both versions of Passed() prevent T from being an lvalue reference. The first 687// via use of enable_if, and the second takes a T* which will not bind to T&. 688template <typename T, 689 typename std::enable_if<internal::IsMoveOnlyType<T>::value && 690 !std::is_lvalue_reference<T>::value>::type* = 691 nullptr> 692static inline internal::PassedWrapper<T> Passed(T&& scoper) { 693 return internal::PassedWrapper<T>(std::move(scoper)); 694} 695template <typename T, 696 typename std::enable_if<internal::IsMoveOnlyType<T>::value>::type* = 697 nullptr> 698static inline internal::PassedWrapper<T> Passed(T* scoper) { 699 return internal::PassedWrapper<T>(std::move(*scoper)); 700} 701 702template <typename T> 703static inline internal::IgnoreResultHelper<T> IgnoreResult(T data) { 704 return internal::IgnoreResultHelper<T>(data); 705} 706 707template <typename T> 708static inline internal::IgnoreResultHelper<Callback<T> > 709IgnoreResult(const Callback<T>& data) { 710 return internal::IgnoreResultHelper<Callback<T> >(data); 711} 712 713BASE_EXPORT void DoNothing(); 714 715template<typename T> 716void DeletePointer(T* obj) { 717 delete obj; 718} 719 720} // namespace base 721 722#endif // BASE_BIND_HELPERS_H_ 723