Handle.hpp

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// The Reactive C++ Toolbox.
// Copyright (C) 2013-2019 Swirly Cloud Limited
// Copyright (C) 2022 Reactive Markets Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef TOOLBOX_IO_HANDLE_HPP
#define TOOLBOX_IO_HANDLE_HPP
 
#include <utility> // swap<>
 
#include <unistd.h> // close()
 
namespace toolbox {
inline namespace io {
 
template <typename PolicyT>
class BasicHandle {
  public:
    using Id = typename PolicyT::Id;
 
    static constexpr Id invalid() noexcept { return PolicyT::invalid(); }
 
    constexpr BasicHandle(std::nullptr_t = nullptr) noexcept {}
    constexpr BasicHandle(Id id) noexcept
    : id_{id}
    {
    }
    ~BasicHandle()
    {
        if (id_ != invalid()) {
            PolicyT::close(id_);
        }
    }
 
    // Copy.
    BasicHandle(const BasicHandle&) = delete;
    BasicHandle& operator=(const BasicHandle&) = delete;
 
    // Move.
    constexpr BasicHandle(BasicHandle&& rhs) noexcept
    : id_{rhs.id_}
    {
        rhs.id_ = invalid();
    }
    BasicHandle& operator=(BasicHandle&& rhs) noexcept
    {
        reset();
        swap(rhs);
        return *this;
    }
 
    constexpr bool empty() const noexcept { return id_ == invalid(); }
    constexpr explicit operator bool() const noexcept { return id_ != invalid(); }
 
    constexpr Id get() const noexcept { return id_; }
    constexpr Id operator*() const noexcept { return get(); }
 
    Id release() noexcept
    {
        const auto id = id_;
        id_ = invalid();
        return id;
    }
    void reset(std::nullptr_t = nullptr) noexcept { reset(invalid()); }
    void reset(Id id) noexcept
    {
        std::swap(id_, id);
        if (id != invalid()) {
            PolicyT::close(id);
        }
    }
    void swap(BasicHandle& rhs) noexcept { std::swap(id_, rhs.id_); }
 
  private:
    Id id_{invalid()};
};
 
template <typename PolicyT>
constexpr bool operator==(const BasicHandle<PolicyT>& lhs, const BasicHandle<PolicyT>& rhs)
{
    return lhs.get() == rhs.get();
}
 
template <typename PolicyT>
constexpr bool operator!=(const BasicHandle<PolicyT>& lhs, const BasicHandle<PolicyT>& rhs)
{
    return !(lhs == rhs);
}
 
struct FilePolicy {
    using Id = int;
    static constexpr int invalid() noexcept { return -1; }
    static void close(int fd) noexcept { ::close(fd); }
};
 
using FileHandle = BasicHandle<FilePolicy>;
 
} // namespace io
} // namespace toolbox
 
#endif // TOOLBOX_IO_HANDLE_HPP