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//===--- Function.h - Utility callable wrappers -----------------*- C++-*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file provides an analogue to std::function that supports move semantics.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_FUNCTION_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_FUNCTION_H
#include "llvm/ADT/STLExtras.h"
#include <cassert>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
namespace clang {
namespace clangd {
/// A move-only type-erasing function wrapper. Similar to `std::function`, but
/// allows to store move-only callables.
template <class> class UniqueFunction;
template <class Ret, class... Args> class UniqueFunction<Ret(Args...)> {
public:
UniqueFunction() = default;
UniqueFunction(std::nullptr_t) : UniqueFunction(){};
UniqueFunction(UniqueFunction const &) = delete;
UniqueFunction &operator=(UniqueFunction const &) = delete;
UniqueFunction(UniqueFunction &&) noexcept = default;
UniqueFunction &operator=(UniqueFunction &&) noexcept = default;
template <class Callable,
/// A sfinae-check that Callable can be called with Args... and
class = typename std::enable_if<std::is_convertible<
decltype(std::declval<Callable>()(std::declval<Args>()...)),
Ret>::value>::type>
UniqueFunction(Callable &&Func)
: CallablePtr(llvm::make_unique<
FunctionCallImpl<typename std::decay<Callable>::type>>(
std::forward<Callable>(Func))) {}
explicit operator bool() { return bool(CallablePtr); }
Ret operator()(Args... As) {
assert(CallablePtr);
return CallablePtr->Call(std::forward<Args>(As)...);
}
private:
class FunctionCallBase {
public:
virtual ~FunctionCallBase() = default;
virtual Ret Call(Args... As) = 0;
};
template <class Callable>
class FunctionCallImpl final : public FunctionCallBase {
static_assert(
std::is_same<Callable, typename std::decay<Callable>::type>::value,
"FunctionCallImpl must be instanstiated with std::decay'ed types");
public:
FunctionCallImpl(Callable Func) : Func(std::move(Func)) {}
Ret Call(Args... As) override { return Func(std::forward<Args>(As)...); }
private:
Callable Func;
};
std::unique_ptr<FunctionCallBase> CallablePtr;
};
/// Stores a callable object (Func) and arguments (Args) and allows to call the
/// callable with provided arguments later using `operator ()`. The arguments
/// are std::forward'ed into the callable in the body of `operator()`. Therefore
/// `operator()` can only be called once, as some of the arguments could be
/// std::move'ed into the callable on first call.
template <class Func, class... Args> struct ForwardBinder {
using Tuple = std::tuple<typename std::decay<Func>::type,
typename std::decay<Args>::type...>;
Tuple FuncWithArguments;
#ifndef NDEBUG
bool WasCalled = false;
#endif
public:
ForwardBinder(Tuple FuncWithArguments)
: FuncWithArguments(std::move(FuncWithArguments)) {}
private:
template <std::size_t... Indexes, class... RestArgs>
auto CallImpl(llvm::integer_sequence<std::size_t, Indexes...> Seq,
RestArgs &&... Rest)
-> decltype(std::get<0>(this->FuncWithArguments)(
std::forward<Args>(std::get<Indexes + 1>(this->FuncWithArguments))...,
std::forward<RestArgs>(Rest)...)) {
return std::get<0>(this->FuncWithArguments)(
std::forward<Args>(std::get<Indexes + 1>(this->FuncWithArguments))...,
std::forward<RestArgs>(Rest)...);
}
public:
template <class... RestArgs>
auto operator()(RestArgs &&... Rest)
-> decltype(this->CallImpl(llvm::index_sequence_for<Args...>(),
std::forward<RestArgs>(Rest)...)) {
#ifndef NDEBUG
assert(!WasCalled && "Can only call result of BindWithForward once.");
WasCalled = true;
#endif
return CallImpl(llvm::index_sequence_for<Args...>(),
std::forward<RestArgs>(Rest)...);
}
};
/// Creates an object that stores a callable (\p F) and first arguments to the
/// callable (\p As) and allows to call \p F with \Args at a later point.
/// Similar to std::bind, but also works with move-only \p F and \p As.
///
/// The returned object must be called no more than once, as \p As are
/// std::forwarded'ed (therefore can be moved) into \p F during the call.
template <class Func, class... Args>
ForwardBinder<Func, Args...> BindWithForward(Func F, Args &&... As) {
return ForwardBinder<Func, Args...>(
std::make_tuple(std::forward<Func>(F), std::forward<Args>(As)...));
}
namespace detail {
/// Runs provided callback in destructor. Use onScopeExit helper function to
/// create this object.
template <class Func> struct ScopeExitGuard {
static_assert(std::is_same<typename std::decay<Func>::type, Func>::value,
"Func must be decayed");
ScopeExitGuard(Func F) : F(std::move(F)) {}
~ScopeExitGuard() {
if (!F)
return;
(*F)();
}
// Move-only.
ScopeExitGuard(const ScopeExitGuard &) = delete;
ScopeExitGuard &operator=(const ScopeExitGuard &) = delete;
ScopeExitGuard(ScopeExitGuard &&Other) = default;
ScopeExitGuard &operator=(ScopeExitGuard &&Other) = default;
private:
llvm::Optional<Func> F;
};
} // namespace detail
/// Creates a RAII object that will run \p F in its destructor.
template <class Func>
auto onScopeExit(Func &&F)
-> detail::ScopeExitGuard<typename std::decay<Func>::type> {
return detail::ScopeExitGuard<typename std::decay<Func>::type>(
std::forward<Func>(F));
}
} // namespace clangd
} // namespace clang
#endif
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