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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 utilities for callable objects.
#include "llvm/ADT/FunctionExtras.h"
#include "llvm/Support/Error.h"
#include <tuple>
#include <utility>
namespace clang {
namespace clangd {
/// A Callback<T> is a void function that accepts Expected<T>.
/// This is accepted by ClangdServer functions that logically return T.
template <typename T>
using Callback = llvm::unique_function<void(llvm::Expected<T>)>;
/// 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;
ForwardBinder(Tuple FuncWithArguments)
: FuncWithArguments(std::move(FuncWithArguments)) {}
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))...,
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 Bind once.");
WasCalled = true;
return CallImpl(llvm::index_sequence_for<Args...>(),
/// 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...> Bind(Func F, Args &&... As) {
return ForwardBinder<Func, Args...>(
std::make_tuple(std::forward<Func>(F), std::forward<Args>(As)...));
} // namespace clangd
} // namespace clang