[llvm] r336156 - [ADT] Add llvm::unique_function which is like std::function but
Chandler Carruth via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 2 16:57:30 PDT 2018
Author: chandlerc
Date: Mon Jul 2 16:57:29 2018
New Revision: 336156
URL: http://llvm.org/viewvc/llvm-project?rev=336156&view=rev
Log:
[ADT] Add llvm::unique_function which is like std::function but
supporting move-only closures.
Most of the core optimizations for std::function are here plus
a potentially novel one that detects trivially movable and destroyable
functors and implements those with fewer indirections.
This is especially useful as we start trying to add concurrency
primitives as those often end up with move-only types (futures,
promises, etc) and wanting them to work through lambdas.
As further work, we could add better support for things like const-qualified
operator()s to support more algorithms, and r-value ref qualified operator()s
to model call-once. None of that is here though.
We can also provide our own llvm::function that has some of the optimizations
used in this class, but with copy semantics instead of move semantics.
This is motivated by increasing usage of things like executors and the task
queue where it is useful to embed move-only types like a std::promise within
a type erased function. That isn't possible without this version of a type
erased function.
Differential Revision: https://reviews.llvm.org/D48349
Added:
llvm/trunk/include/llvm/ADT/FunctionExtras.h
llvm/trunk/unittests/ADT/FunctionExtrasTest.cpp
Modified:
llvm/trunk/include/llvm/Support/Compiler.h
llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h
llvm/trunk/unittests/ADT/CMakeLists.txt
Added: llvm/trunk/include/llvm/ADT/FunctionExtras.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/FunctionExtras.h?rev=336156&view=auto
==============================================================================
--- llvm/trunk/include/llvm/ADT/FunctionExtras.h (added)
+++ llvm/trunk/include/llvm/ADT/FunctionExtras.h Mon Jul 2 16:57:29 2018
@@ -0,0 +1,274 @@
+//===- FunctionExtras.h - Function type erasure utilities -------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file provides a collection of function (or more generally, callable)
+/// type erasure utilities supplementing those provided by the standard library
+/// in `<function>`.
+///
+/// It provides `unique_function`, which works like `std::function` but supports
+/// move-only callable objects.
+///
+/// Future plans:
+/// - Add a `function` that provides const, volatile, and ref-qualified support,
+/// which doesn't work with `std::function`.
+/// - Provide support for specifying multiple signatures to type erase callable
+/// objects with an overload set, such as those produced by generic lambdas.
+/// - Expand to include a copyable utility that directly replaces std::function
+/// but brings the above improvements.
+///
+/// Note that LLVM's utilities are greatly simplified by not supporting
+/// allocators.
+///
+/// If the standard library ever begins to provide comparable facilities we can
+/// consider switching to those.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_FUNCTION_EXTRAS_H
+#define LLVM_ADT_FUNCTION_EXTRAS_H
+
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/PointerUnion.h"
+#include <memory>
+#include <type_traits>
+
+namespace llvm {
+
+template <typename FunctionT> class unique_function;
+
+template <typename ReturnT, typename... ParamTs>
+class unique_function<ReturnT(ParamTs...)> {
+ static constexpr int InlineStorageSize = sizeof(void *) * 3;
+
+ // Provide a type function to map parameters that won't observe extra copies
+ // or moves and which are small enough to likely pass in register to values
+ // and all other types to l-value reference types. We use this to compute the
+ // types used in our erased call utility to minimize copies and moves unless
+ // doing so would force things unnecessarily into memory.
+ //
+ // The heuristic used is related to common ABI register passing conventions.
+ // It doesn't have to be exact though, and in one way it is more strict
+ // because we want to still be able to observe either moves *or* copies.
+ template <typename T>
+ using AdjustedParamT = typename std::conditional<
+ !std::is_reference<T>::value &&
+ std::is_trivially_copy_constructible<T>::value &&
+ std::is_trivially_move_constructible<T>::value &&
+ sizeof(T) <= (2 * sizeof(void *)),
+ T, T &>::type;
+
+ // The type of the erased function pointer we use as a callback to dispatch to
+ // the stored callable when it is trivial to move and destroy.
+ using CallPtrT = ReturnT (*)(void *CallableAddr,
+ AdjustedParamT<ParamTs>... Params);
+ using MovePtrT = void (*)(void *LHSCallableAddr, void *RHSCallableAddr);
+ using DestroyPtrT = void (*)(void *CallableAddr);
+
+ /// A struct we use to aggregate three callbacks when we need full set of
+ /// operations.
+ struct NonTrivialCallbacks {
+ CallPtrT CallPtr;
+ MovePtrT MovePtr;
+ DestroyPtrT DestroyPtr;
+ };
+
+ // Now we can create a pointer union between either a direct, trivial call
+ // pointer and a pointer to a static struct of the call, move, and destroy
+ // pointers. We do this to keep the footprint in this object a single pointer
+ // while supporting all the necessary type-erased operation.
+ using CallbackPointerUnionT = PointerUnion<CallPtrT, NonTrivialCallbacks *>;
+
+ // The main storage buffer. This will either have a pointer to out-of-line
+ // storage or an inline buffer storing the callable.
+ union StorageUnionT {
+ // For out-of-line storage we keep a pointer to the underlying storage and
+ // the size. This is enough to deallocate the memory.
+ struct OutOfLineStorageT {
+ void *StoragePtr;
+ size_t Size;
+ size_t Alignment;
+ } OutOfLineStorage;
+ static_assert(
+ sizeof(OutOfLineStorageT) <= InlineStorageSize,
+ "Should always use all of the out-of-line storage for inline storage!");
+
+ // For in-line storage, we just provide an aligned character buffer. We
+ // provide three pointers worth of storage here.
+ typename std::aligned_storage<InlineStorageSize, alignof(void *)>::type
+ InlineStorage;
+ } StorageUnion;
+
+ // A compressed pointer to either our dispatching callback or our table of
+ // dispatching callbacks and the flag for whether the callable itself is
+ // stored inline or not.
+ PointerIntPair<CallbackPointerUnionT, 1, bool> CallbackAndInlineFlag;
+
+ bool isInlineStorage() const { return CallbackAndInlineFlag.getInt(); }
+
+ bool isTrivialCallback() const {
+ return CallbackAndInlineFlag.getPointer().template is<CallPtrT>();
+ }
+
+ CallPtrT getTrivialCallback() const {
+ return CallbackAndInlineFlag.getPointer().template get<CallPtrT>();
+ }
+
+ NonTrivialCallbacks *getNonTrivialCallbacks() const {
+ return CallbackAndInlineFlag.getPointer()
+ .template get<NonTrivialCallbacks *>();
+ }
+
+ void *getInlineStorage() { return &StorageUnion.InlineStorage; }
+
+ void *getOutOfLineStorage() {
+ return StorageUnion.OutOfLineStorage.StoragePtr;
+ }
+ size_t getOutOfLineStorageSize() const {
+ return StorageUnion.OutOfLineStorage.Size;
+ }
+ size_t getOutOfLineStorageAlignment() const {
+ return StorageUnion.OutOfLineStorage.Alignment;
+ }
+
+ void setOutOfLineStorage(void *Ptr, size_t Size, size_t Alignment) {
+ StorageUnion.OutOfLineStorage = {Ptr, Size, Alignment};
+ }
+
+ template <typename CallableT>
+ static ReturnT CallImpl(void *CallableAddr,
+ AdjustedParamT<ParamTs>... Params) {
+ return (*reinterpret_cast<CallableT *>(CallableAddr))(
+ std::forward<ParamTs>(Params)...);
+ }
+
+ template <typename CallableT>
+ static void MoveImpl(void *LHSCallableAddr, void *RHSCallableAddr) noexcept {
+ new (LHSCallableAddr)
+ CallableT(std::move(*reinterpret_cast<CallableT *>(RHSCallableAddr)));
+ }
+
+ template <typename CallableT>
+ static void DestroyImpl(void *CallableAddr) noexcept {
+ reinterpret_cast<CallableT *>(CallableAddr)->~CallableT();
+ }
+
+public:
+ unique_function() = default;
+ unique_function(std::nullptr_t /*null_callable*/) {}
+
+ ~unique_function() {
+ if (!CallbackAndInlineFlag.getPointer())
+ return;
+
+ // Cache this value so we don't re-check it after type-erased operations.
+ bool IsInlineStorage = isInlineStorage();
+
+ if (!isTrivialCallback())
+ getNonTrivialCallbacks()->DestroyPtr(
+ IsInlineStorage ? getInlineStorage() : getOutOfLineStorage());
+
+ if (!IsInlineStorage)
+ deallocate_buffer(getOutOfLineStorage(), getOutOfLineStorageSize(),
+ getOutOfLineStorageAlignment());
+ }
+
+ unique_function(unique_function &&RHS) noexcept {
+ // Copy the callback and inline flag.
+ CallbackAndInlineFlag = RHS.CallbackAndInlineFlag;
+
+ // If the RHS is empty, just copying the above is sufficient.
+ if (!RHS)
+ return;
+
+ if (!isInlineStorage()) {
+ // The out-of-line case is easiest to move.
+ StorageUnion.OutOfLineStorage = RHS.StorageUnion.OutOfLineStorage;
+ } else if (isTrivialCallback()) {
+ // Move is trivial, just memcpy the bytes across.
+ memcpy(getInlineStorage(), RHS.getInlineStorage(), InlineStorageSize);
+ } else {
+ // Non-trivial move, so dispatch to a type-erased implementation.
+ getNonTrivialCallbacks()->MovePtr(getInlineStorage(),
+ RHS.getInlineStorage());
+ }
+
+ // Clear the old callback and inline flag to get back to as-if-null.
+ RHS.CallbackAndInlineFlag = {};
+
+#ifndef NDEBUG
+ // In debug builds, we also scribble across the rest of the storage.
+ memset(RHS.getInlineStorage(), 0xAD, InlineStorageSize);
+#endif
+ }
+
+ unique_function &operator=(unique_function &&RHS) noexcept {
+ if (this == &RHS)
+ return *this;
+
+ // Because we don't try to provide any exception safety guarantees we can
+ // implement move assignment very simply by first destroying the current
+ // object and then move-constructing over top of it.
+ this->~unique_function();
+ new (this) unique_function(std::move(RHS));
+ return *this;
+ }
+
+ template <typename CallableT> unique_function(CallableT Callable) {
+ bool IsInlineStorage = true;
+ void *CallableAddr = getInlineStorage();
+ if (sizeof(CallableT) > InlineStorageSize ||
+ alignof(CallableT) > alignof(decltype(StorageUnion.InlineStorage))) {
+ IsInlineStorage = false;
+ // Allocate out-of-line storage. FIXME: Use an explicit alignment
+ // parameter in C++17 mode.
+ auto Size = sizeof(CallableT);
+ auto Alignment = alignof(CallableT);
+ CallableAddr = allocate_buffer(Size, Alignment);
+ setOutOfLineStorage(CallableAddr, Size, Alignment);
+ }
+
+ // Now move into the storage.
+ new (CallableAddr) CallableT(std::move(Callable));
+
+ // See if we can create a trivial callback.
+ // FIXME: we should use constexpr if here and below to avoid instantiating
+ // the non-trivial static objects when unnecessary. While the linker should
+ // remove them, it is still wasteful.
+ if (std::is_trivially_move_constructible<CallableT>::value &&
+ std::is_trivially_destructible<CallableT>::value) {
+ CallbackAndInlineFlag = {&CallImpl<CallableT>, IsInlineStorage};
+ return;
+ }
+
+ // Otherwise, we need to point at an object with a vtable that contains all
+ // the different type erased behaviors needed. Create a static instance of
+ // the derived type here and then use a pointer to that.
+ static NonTrivialCallbacks Callbacks = {
+ &CallImpl<CallableT>, &MoveImpl<CallableT>, &DestroyImpl<CallableT>};
+
+ CallbackAndInlineFlag = {&Callbacks, IsInlineStorage};
+ }
+
+ ReturnT operator()(ParamTs... Params) {
+ void *CallableAddr =
+ isInlineStorage() ? getInlineStorage() : getOutOfLineStorage();
+
+ return (isTrivialCallback()
+ ? getTrivialCallback()
+ : getNonTrivialCallbacks()->CallPtr)(CallableAddr, Params...);
+ }
+
+ explicit operator bool() const {
+ return (bool)CallbackAndInlineFlag.getPointer();
+ }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_FUNCTION_H
Modified: llvm/trunk/include/llvm/Support/Compiler.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Compiler.h?rev=336156&r1=336155&r2=336156&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/Compiler.h (original)
+++ llvm/trunk/include/llvm/Support/Compiler.h Mon Jul 2 16:57:29 2018
@@ -17,6 +17,9 @@
#include "llvm/Config/llvm-config.h"
+#include <new>
+#include <stddef.h>
+
#if defined(_MSC_VER)
#include <sal.h>
#endif
@@ -503,4 +506,46 @@ void AnnotateIgnoreWritesEnd(const char
#define LLVM_ENABLE_EXCEPTIONS 1
#endif
+namespace llvm {
+
+/// Allocate a buffer of memory with the given size and alignment.
+///
+/// When the compiler supports aligned operator new, this will use it to to
+/// handle even over-aligned allocations.
+///
+/// However, this doesn't make any attempt to leverage the fancier techniques
+/// like posix_memalign due to portability. It is mostly intended to allow
+/// compatibility with platforms that, after aligned allocation was added, use
+/// reduced default alignment.
+inline void *allocate_buffer(size_t Size, size_t Alignment) {
+ return ::operator new(Size
+#if __cpp_aligned_new
+ ,
+ std::align_val_t(Alignment)
+#endif
+ );
+}
+
+/// Deallocate a buffer of memory with the given size and alignment.
+///
+/// If supported, this will used the sized delete operator. Also if supported,
+/// this will pass the alignment to the delete operator.
+///
+/// The pointer must have been allocated with the corresponding new operator,
+/// most likely using the above helper.
+inline void deallocate_buffer(void *Ptr, size_t Size, size_t Alignment) {
+ ::operator delete(Ptr
+#if __cpp_sized_deallocation
+ ,
+ Size
+#endif
+#if __cpp_aligned_new
+ ,
+ std::align_val_t(Alignment)
+#endif
+ );
+}
+
+} // End namespace llvm
+
#endif
Modified: llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h?rev=336156&r1=336155&r2=336156&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h (original)
+++ llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h Mon Jul 2 16:57:29 2018
@@ -16,6 +16,7 @@
#define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
#include "llvm/Support/DataTypes.h"
+#include <assert.h>
#include <type_traits>
namespace llvm {
@@ -111,6 +112,39 @@ template <> struct PointerLikeTypeTraits
enum { NumLowBitsAvailable = 0 };
};
+/// Provide suitable custom traits struct for function pointers.
+///
+/// Function pointers can't be directly given these traits as functions can't
+/// have their alignment computed with `alignof` and we need different casting.
+///
+/// To rely on higher alignment for a specialized use, you can provide a
+/// customized form of this template explicitly with higher alignment, and
+/// potentially use alignment attributes on functions to satisfy that.
+template <int Alignment, typename FunctionPointerT>
+struct FunctionPointerLikeTypeTraits {
+ enum { NumLowBitsAvailable = detail::ConstantLog2<Alignment>::value };
+ static inline void *getAsVoidPointer(FunctionPointerT P) {
+ assert((reinterpret_cast<uintptr_t>(P) &
+ ~((uintptr_t)-1 << NumLowBitsAvailable)) == 0 &&
+ "Alignment not satisfied for an actual function pointer!");
+ return reinterpret_cast<void *>(P);
+ }
+ static inline FunctionPointerT getFromVoidPointer(void *P) {
+ return reinterpret_cast<FunctionPointerT>(P);
+ }
+};
+
+/// Provide a default specialization for function pointers that assumes 4-byte
+/// alignment.
+///
+/// We assume here that functions used with this are always at least 4-byte
+/// aligned. This means that, for example, thumb functions won't work or systems
+/// with weird unaligned function pointers won't work. But all practical systems
+/// we support satisfy this requirement.
+template <typename ReturnT, typename... ParamTs>
+struct PointerLikeTypeTraits<ReturnT (*)(ParamTs...)>
+ : FunctionPointerLikeTypeTraits<4, ReturnT (*)(ParamTs...)> {};
+
} // end namespace llvm
#endif
Modified: llvm/trunk/unittests/ADT/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/CMakeLists.txt?rev=336156&r1=336155&r2=336156&view=diff
==============================================================================
--- llvm/trunk/unittests/ADT/CMakeLists.txt (original)
+++ llvm/trunk/unittests/ADT/CMakeLists.txt Mon Jul 2 16:57:29 2018
@@ -18,6 +18,7 @@ add_llvm_unittest(ADTTests
DepthFirstIteratorTest.cpp
EquivalenceClassesTest.cpp
FoldingSet.cpp
+ FunctionExtrasTest.cpp
FunctionRefTest.cpp
HashingTest.cpp
IListBaseTest.cpp
Added: llvm/trunk/unittests/ADT/FunctionExtrasTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/FunctionExtrasTest.cpp?rev=336156&view=auto
==============================================================================
--- llvm/trunk/unittests/ADT/FunctionExtrasTest.cpp (added)
+++ llvm/trunk/unittests/ADT/FunctionExtrasTest.cpp Mon Jul 2 16:57:29 2018
@@ -0,0 +1,228 @@
+//===- FunctionExtrasTest.cpp - Unit tests for function type erasure ------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/FunctionExtras.h"
+#include "gtest/gtest.h"
+
+#include <memory>
+
+using namespace llvm;
+
+namespace {
+
+TEST(UniqueFunctionTest, Basic) {
+ unique_function<int(int, int)> Sum = [](int A, int B) { return A + B; };
+ EXPECT_EQ(Sum(1, 2), 3);
+
+ unique_function<int(int, int)> Sum2 = std::move(Sum);
+ EXPECT_EQ(Sum2(1, 2), 3);
+
+ unique_function<int(int, int)> Sum3 = [](int A, int B) { return A + B; };
+ Sum2 = std::move(Sum3);
+ EXPECT_EQ(Sum2(1, 2), 3);
+
+ Sum2 = unique_function<int(int, int)>([](int A, int B) { return A + B; });
+ EXPECT_EQ(Sum2(1, 2), 3);
+
+ // Explicit self-move test.
+ *&Sum2 = std::move(Sum2);
+ EXPECT_EQ(Sum2(1, 2), 3);
+
+ Sum2 = unique_function<int(int, int)>();
+ EXPECT_FALSE(Sum2);
+
+ // Make sure we can forward through l-value reference parameters.
+ unique_function<void(int &)> Inc = [](int &X) { ++X; };
+ int X = 42;
+ Inc(X);
+ EXPECT_EQ(X, 43);
+
+ // Make sure we can forward through r-value reference parameters with
+ // move-only types.
+ unique_function<int(std::unique_ptr<int> &&)> ReadAndDeallocByRef =
+ [](std::unique_ptr<int> &&Ptr) {
+ int V = *Ptr;
+ Ptr.reset();
+ return V;
+ };
+ std::unique_ptr<int> Ptr{new int(13)};
+ EXPECT_EQ(ReadAndDeallocByRef(std::move(Ptr)), 13);
+ EXPECT_FALSE((bool)Ptr);
+
+ // Make sure we can pass a move-only temporary as opposed to a local variable.
+ EXPECT_EQ(ReadAndDeallocByRef(std::unique_ptr<int>(new int(42))), 42);
+
+ // Make sure we can pass a move-only type by-value.
+ unique_function<int(std::unique_ptr<int>)> ReadAndDeallocByVal =
+ [](std::unique_ptr<int> Ptr) {
+ int V = *Ptr;
+ Ptr.reset();
+ return V;
+ };
+ Ptr.reset(new int(13));
+ EXPECT_EQ(ReadAndDeallocByVal(std::move(Ptr)), 13);
+ EXPECT_FALSE((bool)Ptr);
+
+ EXPECT_EQ(ReadAndDeallocByVal(std::unique_ptr<int>(new int(42))), 42);
+}
+
+TEST(UniqueFunctionTest, Captures) {
+ long A = 1, B = 2, C = 3, D = 4, E = 5;
+
+ unique_function<long()> Tmp;
+
+ unique_function<long()> C1 = [A]() { return A; };
+ EXPECT_EQ(C1(), 1);
+ Tmp = std::move(C1);
+ EXPECT_EQ(Tmp(), 1);
+
+ unique_function<long()> C2 = [A, B]() { return A + B; };
+ EXPECT_EQ(C2(), 3);
+ Tmp = std::move(C2);
+ EXPECT_EQ(Tmp(), 3);
+
+ unique_function<long()> C3 = [A, B, C]() { return A + B + C; };
+ EXPECT_EQ(C3(), 6);
+ Tmp = std::move(C3);
+ EXPECT_EQ(Tmp(), 6);
+
+ unique_function<long()> C4 = [A, B, C, D]() { return A + B + C + D; };
+ EXPECT_EQ(C4(), 10);
+ Tmp = std::move(C4);
+ EXPECT_EQ(Tmp(), 10);
+
+ unique_function<long()> C5 = [A, B, C, D, E]() { return A + B + C + D + E; };
+ EXPECT_EQ(C5(), 15);
+ Tmp = std::move(C5);
+ EXPECT_EQ(Tmp(), 15);
+}
+
+TEST(UniqueFunctionTest, MoveOnly) {
+ struct SmallCallable {
+ std::unique_ptr<int> A{new int(1)};
+
+ int operator()(int B) { return *A + B; }
+ };
+ unique_function<int(int)> Small = SmallCallable();
+ EXPECT_EQ(Small(2), 3);
+ unique_function<int(int)> Small2 = std::move(Small);
+ EXPECT_EQ(Small2(2), 3);
+
+ struct LargeCallable {
+ std::unique_ptr<int> A{new int(1)};
+ std::unique_ptr<int> B{new int(2)};
+ std::unique_ptr<int> C{new int(3)};
+ std::unique_ptr<int> D{new int(4)};
+ std::unique_ptr<int> E{new int(5)};
+
+ int operator()() { return *A + *B + *C + *D + *E; }
+ };
+ unique_function<int()> Large = LargeCallable();
+ EXPECT_EQ(Large(), 15);
+ unique_function<int()> Large2 = std::move(Large);
+ EXPECT_EQ(Large2(), 15);
+}
+
+TEST(UniqueFunctionTest, CountForwardingCopies) {
+ struct CopyCounter {
+ int &CopyCount;
+
+ CopyCounter(int &CopyCount) : CopyCount(CopyCount) {}
+ CopyCounter(const CopyCounter &Arg) : CopyCount(Arg.CopyCount) {
+ ++CopyCount;
+ }
+ };
+
+ unique_function<void(CopyCounter)> ByValF = [](CopyCounter) {};
+ int CopyCount = 0;
+ ByValF(CopyCounter(CopyCount));
+ EXPECT_EQ(1, CopyCount);
+
+ CopyCount = 0;
+ {
+ CopyCounter Counter{CopyCount};
+ ByValF(Counter);
+ }
+ EXPECT_EQ(2, CopyCount);
+
+ // Check that we don't generate a copy at all when we can bind a reference all
+ // the way down, even if that reference could *in theory* allow copies.
+ unique_function<void(const CopyCounter &)> ByRefF = [](const CopyCounter &) {
+ };
+ CopyCount = 0;
+ ByRefF(CopyCounter(CopyCount));
+ EXPECT_EQ(0, CopyCount);
+
+ CopyCount = 0;
+ {
+ CopyCounter Counter{CopyCount};
+ ByRefF(Counter);
+ }
+ EXPECT_EQ(0, CopyCount);
+
+ // If we use a reference, we can make a stronger guarantee that *no* copy
+ // occurs.
+ struct Uncopyable {
+ Uncopyable() = default;
+ Uncopyable(const Uncopyable &) = delete;
+ };
+ unique_function<void(const Uncopyable &)> UncopyableF =
+ [](const Uncopyable &) {};
+ UncopyableF(Uncopyable());
+ Uncopyable X;
+ UncopyableF(X);
+}
+
+TEST(UniqueFunctionTest, CountForwardingMoves) {
+ struct MoveCounter {
+ int &MoveCount;
+
+ MoveCounter(int &MoveCount) : MoveCount(MoveCount) {}
+ MoveCounter(MoveCounter &&Arg) : MoveCount(Arg.MoveCount) { ++MoveCount; }
+ };
+
+ unique_function<void(MoveCounter)> ByValF = [](MoveCounter) {};
+ int MoveCount = 0;
+ ByValF(MoveCounter(MoveCount));
+ EXPECT_EQ(1, MoveCount);
+
+ MoveCount = 0;
+ {
+ MoveCounter Counter{MoveCount};
+ ByValF(std::move(Counter));
+ }
+ EXPECT_EQ(2, MoveCount);
+
+ // Check that when we use an r-value reference we get no spurious copies.
+ unique_function<void(MoveCounter &&)> ByRefF = [](MoveCounter &&) {};
+ MoveCount = 0;
+ ByRefF(MoveCounter(MoveCount));
+ EXPECT_EQ(0, MoveCount);
+
+ MoveCount = 0;
+ {
+ MoveCounter Counter{MoveCount};
+ ByRefF(std::move(Counter));
+ }
+ EXPECT_EQ(0, MoveCount);
+
+ // If we use an r-value reference we can in fact make a stronger guarantee
+ // with an unmovable type.
+ struct Unmovable {
+ Unmovable() = default;
+ Unmovable(Unmovable &&) = delete;
+ };
+ unique_function<void(const Unmovable &)> UnmovableF = [](const Unmovable &) {
+ };
+ UnmovableF(Unmovable());
+ Unmovable X;
+ UnmovableF(X);
+}
+
+} // anonymous namespace
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