MovableEnvelope.h

#ifndef _MovableEnvelope_h_
#define _MovableEnvelope_h_

#include "../util/Logger.h"

#include <boost/spirit/include/support_argument.hpp>

#include <memory>
#include <type_traits>

namespace parse::detail {
    /** \p MovableEnvelope enables the boost::spirit parser to handle a
        \p T with move semantics.

        boost::spirit is designed only work with value semantics. The
        boost::phoenix actors only handle value semantics.  Types with move
        only semantics like unique_ptr will not work as expected.

        boost::spirit is designed to work with compile time polymorphism.  With
        run-time polymorphism using raw pointers to track heap objects, each
        time the parser backtracks it leaks memory.

        \p MovableEnvelope makes a \p unique_ptr<T> with move only semantics
        appear to have copy semantics, by moving it each time that it is copied.
        This allows boost::phoenix actors to handle it correctly if the movement is
        one way from creation at the parse location to consumption in a larger
        parsed component.

        \p MovableEnvelope is a work around.  It can be removed if
        boost::spirit supports move semantics, or the parser is changed to use
        compile time polymorphism.
    */
    template <typename T>
    class MovableEnvelope {
    public:
        using enveloped_type = T;

        /** \name Rule of Five constructors and operators.
            MovableEnvelope satisfies the rule of five with the following
            constructors and operator=().
         */ //@{

        // Default constructor
        MovableEnvelope() {}

        // Copy constructor
        // This leaves \p other in an emptied state
        MovableEnvelope(const MovableEnvelope& other) :
            MovableEnvelope(std::move(other.obj))
        {}

        // Move constructor
        MovableEnvelope(MovableEnvelope&& other) :
            MovableEnvelope(std::move(other.obj))
        {}

        // Move operator
        MovableEnvelope& operator= (MovableEnvelope&& other) {
            obj = std::move(other.obj);
            original_obj = other.original_obj;
            // Intentionally leave other.original_obj != other.obj.get()
            return *this;
        }

        // Copy operator
        // This leaves \p other in an emptied state
        MovableEnvelope& operator= (const MovableEnvelope& other) {
            obj = std::move(other.obj);
            original_obj = other.original_obj;
            // Intentionally leave other.original_obj != other.obj.get()
            return *this;
        }
        //@}

        virtual ~MovableEnvelope() = default;

        /** \name Converting constructors and operators.
            MovableEnvelope allows conversion between compatible types with the following
            constructors and operators.
         */ //@{

        // nullptr constructor
        MovableEnvelope(std::nullptr_t) {}

        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        explicit MovableEnvelope(std::unique_ptr<U>&& obj_) :
            obj(std::move(obj_)),
            original_obj(obj.get())
        {}

        // This takes ownership of obj_
        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        explicit MovableEnvelope(U* obj_) :
            obj(obj_),
            original_obj(obj.get())
        {}

        // Converting copy constructor
        // This leaves \p other in an emptied state
        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        MovableEnvelope(const MovableEnvelope<U>& other) :
            MovableEnvelope(std::move(other.obj))
        {}

        // Converting move constructor
        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        MovableEnvelope(MovableEnvelope<U>&& other) :
            MovableEnvelope(std::move(other.obj))
        {}

        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        MovableEnvelope& operator= (MovableEnvelope<U>&& other) {
            obj = std::move(other.obj);
            original_obj = other.original_obj;
            // Intentionally leave other.original_obj != other.obj.get()
            return *this;
        }

        // Copy operator
        // This leaves \p other in an emptied state
        template <typename U> requires (std::is_convertible_v<std::unique_ptr<U>, std::unique_ptr<T>>)
        MovableEnvelope& operator= (const MovableEnvelope<U>& other) {
            obj = std::move(other.obj);
            original_obj = other.original_obj;
            // Intentionally leave other.original_obj != other.obj.get()
            return *this;
        }
        //@}

        // Return false if the original \p obj has been moved away from this
        // MovableEnvelope.
        bool IsEmptiedEnvelope() const
        { return (original_obj != obj.get());}

        /** OpenEnvelope returns the enclosed \p obj and throws an expectation
            exception if the wrapped pointer was already moved out of this \p
            MovableEnvelope.

            \p OpenEnvelope is a one-shot.  Calling OpenEnvelope a second time
            will throw, since the obj has already been removed.

            \p pass should refer to qi::_pass_type to facilitate the
            expectation exception.
        */

        std::unique_ptr<T> OpenEnvelope(bool& pass) const {
            if (IsEmptiedEnvelope()) {
                ErrorLogger() <<
                    "The parser attempted to extract the unique_ptr from a MovableEnvelope more than once. "
                    "Until boost::spirit supports move semantics MovableEnvelope requires that unique_ptr be used only once. "
                    "Check that a parser is not back tracking over an actor containing an opened MovableEnvelope. "
                    "Check that set, map or vector parses are not repeatedly extracting the same unique_ptr<T>.";

                pass = false;
            }
            return std::move(obj);
        }

    private:
        template <typename U>
        friend class MovableEnvelope;

        mutable std::unique_ptr<T> obj;

        mutable T* original_obj = nullptr;
    };

    /** \p construct_movable is a functor that constructs a MovableEnvelope<T> */
    struct construct_movable {
        template <typename T>
        using result_type = MovableEnvelope<T>;

        template <typename T>
        result_type<T> operator() (T* obj) const
        { return MovableEnvelope<T>(obj); }

        template <typename T>
        result_type<T> operator() (std::unique_ptr<T>&& obj) const
        { return MovableEnvelope<T>(std::move(obj)); }

        template <typename T>
        result_type<T> operator() (std::unique_ptr<T>& obj) const
        { return MovableEnvelope<T>(std::move(obj)); }

        template <typename T>
        result_type<T> operator() (MovableEnvelope<T>&& obj) const
        { return MovableEnvelope<T>(std::move(obj)); }

        template <typename T>
        result_type<T> operator() (const MovableEnvelope<T>& obj) const
        { return MovableEnvelope<T>(obj); }
    };

    /** Free functions converting containers of MovableEnvelope to unique_ptrs. */
    template <typename T>
    std::vector<std::unique_ptr<T>> OpenEnvelopes(const std::vector<MovableEnvelope<T>>& envelopes,
                                                  bool& pass)
    {
        std::vector<std::unique_ptr<T>> retval;
        retval.reserve(envelopes.size());
        for (auto&& envelope : envelopes)
            retval.emplace_back(envelope.OpenEnvelope(pass));
        return retval;
    }

    template <typename T>
    std::vector<std::pair<std::string, std::unique_ptr<T>>> OpenEnvelopes(
        const std::vector<std::pair<std::string, MovableEnvelope<T>>>& in, bool& pass)
    {
        std::vector<std::pair<std::string, std::unique_ptr<T>>> retval;
        retval.reserve(in.size());
        for (auto&& name_and_value : in)
            retval.emplace_back(name_and_value.first, name_and_value.second.OpenEnvelope(pass));
        return retval;
    }

    template <typename K, typename V>
    std::map<K, std::unique_ptr<V>> OpenEnvelopes(const std::map<K, MovableEnvelope<V>>& in,
                                                  bool& pass)
    {
        std::map<K, std::unique_ptr<V>> retval;
        for (auto&& name_and_value : in)
            retval.emplace(name_and_value.first, name_and_value.second.OpenEnvelope(pass));
        return retval;
    }


    /**
       Note: This simpler to use version of deconstruct_movable works with clang
       version 4.0.1 and gcc version 7.2.1 with boost 1.63. It does not work
       with clang 3.6.0 or gcc 4.8.4 or MSVC2015, with boost 1.58 on the
       continuous integration servers.  It is because of improved support for
       decltype in the newer compilers.

       When the project moves the required versions past these versions this
       simpler, more uniform code could be adopted.

    / ** \p deconstruct_movable is a functor that extracts the unique_ptr from a
        MovableEnvelope<T>.  This is a one time operation that empties the
        MovableEnvelope<T>.  It is typically done while calling the constructor
        from outside of boost::spirit that expects a unique_ptr<T> */
    class deconstruct_movable_simple_version_that_works_gcc7p2p1_and_clang4p0p1 {
    public:
        template <typename T>
        std::unique_ptr<T> operator() (const MovableEnvelope<T>& obj, bool& pass) const
        { return obj.OpenEnvelope(pass); }

        template <typename T>
        std::vector<std::unique_ptr<T>> operator() (const std::vector<MovableEnvelope<T>>& objs, bool& pass) const
        { return OpenEnvelopes(objs, pass); }

        template <typename T>
        std::vector<std::pair<std::string, std::unique_ptr<T>>> operator() (
            const std::vector<std::pair<std::string, MovableEnvelope<T>>>& objs, bool& pass)
        { return OpenEnvelopes(objs, pass); }
    };

    class deconstruct_movable {
    public:
        template <typename> struct result;

        template <typename F, typename MovableEnvelope_T, typename Bool>
        struct result<F(MovableEnvelope_T, Bool)> {
            using type = std::unique_ptr<typename std::decay_t<MovableEnvelope_T>::enveloped_type>;
        };
        template <typename FMETB>
        using result_t = typename result<FMETB>::type;

        template <typename T>
        result_t<const deconstruct_movable(const MovableEnvelope<T>&, bool&)>
        operator()(const MovableEnvelope<T>& obj, bool& pass) const
        { return obj.OpenEnvelope(pass); }

        template <typename T>
        result_t<const deconstruct_movable(const MovableEnvelope<T>&, bool&)>
        operator()(const MovableEnvelope<T>& obj, const bool& pass) const
        {
            // Note: this ignores the constness of pass because older compilers
            // pass the incorrect constness.
            return obj.OpenEnvelope(pass);
        }

        // Unwrap ::optional<MovablelEnvelope<T>> to return
        // unique_ptr(nullptr) for none
        template <typename T>
        result_t<const deconstruct_movable(const MovableEnvelope<T>&, bool&)>
        operator()(const boost::optional<MovableEnvelope<T>>& obj, bool& pass) const
        {
            if (!obj)
                return nullptr;
            return obj->OpenEnvelope(pass);
        }

        template <typename T>
        result_t<const deconstruct_movable(const MovableEnvelope<T>&, bool&)>
        operator()(const boost::optional<MovableEnvelope<T>>& obj, const bool& pass) const
        {
            // Note: this ignores the constness of pass because older compilers
            // pass the incorrect constness.
            if (!obj)
                return nullptr;
            return obj->OpenEnvelope(pass);
        }
    };

    class deconstruct_movable_vector {
    public:
        template <typename> struct result;

        template <typename F, typename MovableEnvelope_T, typename Bool>
        struct result<F(MovableEnvelope_T, Bool)> {
            using type = std::vector<std::unique_ptr<typename std::decay_t<MovableEnvelope_T>::value_type::enveloped_type>>;
        };
        template <typename FMETB>
        using result_t = typename result<FMETB>::type;

        template <typename T>
        result_t<const deconstruct_movable(const std::vector<MovableEnvelope<T>>&, bool&)>
        operator()(const std::vector<MovableEnvelope<T>>& objs, bool& pass) const
        { return OpenEnvelopes(objs, pass); }

        template <typename T>
        result_t<const deconstruct_movable(const std::vector<MovableEnvelope<T>>&, bool&)>
        operator()(const std::vector<MovableEnvelope<T>>& objs, const bool& pass) const
        {
            // Note: this ignores the constness of pass because older compilers
            // pass the incorrect constness.
            return OpenEnvelopes(objs, pass);
        }

        // Unwrap ::optional<vector<MovablelEnvelope<T>>> and return
        // an empty vector for none
        template <typename T>
        result_t<const deconstruct_movable(const std::vector<MovableEnvelope<T>>&, bool&)>
        operator()(const boost::optional<std::vector<MovableEnvelope<T>>>& objs, bool& pass) const
        {
            if (!objs)
                return {};
            return OpenEnvelopes(*std::move(objs), pass);
        }

        template <typename T>
        result_t<const deconstruct_movable(const std::vector<MovableEnvelope<T>>&, bool&)>
        operator()(const boost::optional<std::vector<MovableEnvelope<T>>>& objs, const bool& pass) const
        {
            // Note: this ignores the constness of pass because older compilers
            // pass the incorrect constness.
            if (!objs)
                return {};
            return OpenEnvelopes(*std::move(objs), pass);
        }
    };

    class deconstruct_movable_vector_pair {
    public:
        template <typename> struct result;

        template <typename F, typename MovableEnvelope_T, typename Bool>
        struct result<F(MovableEnvelope_T, Bool)> {
            using type = std::vector<
                std::pair<std::string,
                          std::unique_ptr<typename std::decay_t<MovableEnvelope_T>::value_type::second_type::enveloped_type>>>;
        };
        template <typename FMETB>
        using result_t = typename result<FMETB>::type;

        template <typename T>
        result_t<const deconstruct_movable(
            const std::vector<std::pair<std::string, MovableEnvelope<T>>>&, bool&)>
        operator()(const std::vector<std::pair<std::string, MovableEnvelope<T>>>& objs, bool& pass) const
        { return OpenEnvelopes(objs, pass); }

        template <typename T>
        result_t<const deconstruct_movable(const std::vector<std::pair<std::string, MovableEnvelope<T>>>&, bool&)>
        operator()(const std::vector<std::pair<std::string, MovableEnvelope<T>>>& objs, const bool& pass) const
        {
            // Note: this ignores the constness of pass because older compilers
            // pass the incorrect constness.
            return OpenEnvelopes(objs, pass);
        }
    };
}


#endif