vmap/libs/generic/callback.h

/*
   Copyright (C) 2001-2006, William Joseph.
   All Rights Reserved.

   This file is part of GtkRadiant.

   GtkRadiant is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   GtkRadiant is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GtkRadiant; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#if !defined( INCLUDED_GENERIC_CLOSURE_H )
#define INCLUDED_GENERIC_CLOSURE_H

/// \file
/// \brief Type-safe techniques for binding the first argument of an opaque callback.

#include <cstddef>
#include "functional.h"

namespace detail {

	template<typename Thunk_>
	class CallbackBase {
		void *m_environment;
		Thunk_ m_thunk;
	public:
		typedef Thunk_ Thunk;

		CallbackBase(void *environment, Thunk function) : m_environment(environment), m_thunk(function) {
		}

		void *getEnvironment() const {
			return m_environment;
		}

		Thunk getThunk() const {
			return m_thunk;
		}
	};

	template<typename Thunk>
	inline bool operator==(const CallbackBase<Thunk> &self, const CallbackBase<Thunk> &other) {
		return self.getEnvironment() == other.getEnvironment() && self.getThunk() == other.getThunk();
	}

	template<typename Thunk>
	inline bool operator!=(const CallbackBase<Thunk> &self, const CallbackBase<Thunk> &other) {
		return !(self == other);
	}

	template<typename Thunk>
	inline bool operator<(const CallbackBase<Thunk> &self, const CallbackBase<Thunk> &other) {
		return self.getEnvironment() < other.getEnvironment() ||
			   (!(other.getEnvironment() < self.getEnvironment()) && self.getThunk() < other.getThunk());
	}

}

namespace detail {

	template<class Type>
	struct ConvertFromOpaque {
	};

	// reference

	template<class T>
	inline const void *convertToOpaque(const T &t) {
		return &t;
	}

	template<class T>
	struct ConvertFromOpaque<const T &> {
		static T const &apply(void *p) {
			return *static_cast<const T *>(p);
		}
	};

	template<class T>
	inline void *convertToOpaque(T &t) {
		return &t;
	}

	template<class T>
	struct ConvertFromOpaque<T &> {
		static T &apply(void *p) {
			return *static_cast<T *>( p );
		}
	};

	// pointer

	template<class T>
	inline const void *convertToOpaque(const T *t) {
		return t;
	}

	template<class T>
	struct ConvertFromOpaque<const T *> {
		static const T *apply(void *p) {
			return static_cast<const T *>(p);
		}
	};

	template<class T>
	inline void *convertToOpaque(T *t) {
		return t;
	}

	template<class T>
	struct ConvertFromOpaque<T *> {
		static T *apply(void *p) {
			return static_cast<T *>(p);
		}
	};

	// function pointer

	template<class R, class... Ts>
	inline const void *convertToOpaque(R(*const &t)(Ts...)) {
		return &t;
	}

	template<class R, class... Ts>
	struct ConvertFromOpaque<R(*const &)(Ts...)> {
		using Type = R(*)(Ts...);

		static Type const &apply(void *p) {
			return *static_cast<Type *>(p);
		}
	};

    template<class R, class... Ts>
    inline void *convertToOpaque(R(*&t)(Ts...)) {
        return &t;
    }

    template<class R, class... Ts>
    struct ConvertFromOpaque<R(*&)(Ts...)> {
        using Type = R(*)(Ts...);

        static Type &apply(void *p) {
            return *static_cast<Type *>(p);
        }
    };

	template<class Caller, class F>
	class BindFirstOpaqueN;

	template<class Caller, class R, class FirstBound, class... Ts>
	class BindFirstOpaqueN<Caller, R(FirstBound, Ts...)> {
		FirstBound firstBound;
	public:
		explicit BindFirstOpaqueN(FirstBound firstBound) : firstBound(firstBound) {
		}

		R operator()(Ts... args) const {
			return Caller::call(firstBound, args...);
		}

		FirstBound getBound() const {
			return firstBound;
		}

		static R thunk(void *environment, Ts... args) {
			return thunk_(detail::ConvertFromOpaque<FirstBound>::apply(environment), args...);
		}

		static R thunk_(FirstBound environment, Ts... args) {
			return Caller::call(environment, args...);
		}

		void *getEnvironment() const {
			return const_cast<void *>(detail::convertToOpaque(firstBound));
		}
	};

}

template<class Caller>
using BindFirstOpaque = detail::BindFirstOpaqueN<Caller, get_func<Caller>>;

/// \brief Combines a void pointer with a pointer to a function which operates on a void pointer.
///
/// Use with the callback constructors MemberCaller0, ConstMemberCaller0, ReferenceCaller0, ConstReferenceCaller0, PointerCaller0, ConstPointerCaller0 and FreeCaller0.
template<class F>
class Callback;

template<class R, class... Ts>
class Callback<R(Ts...)> : public detail::CallbackBase<R(*)(void *, Ts...)> {
	using Base = detail::CallbackBase<R (*)(void *, Ts...)>;

	static R nullThunk(void *, Ts...) {
	}

public:
	using func = R(Ts...);

	Callback() : Base(0, nullThunk) {
	}

	template<typename Caller>
	Callback(const BindFirstOpaque<Caller> &caller) : Base(caller.getEnvironment(), BindFirstOpaque<Caller>::thunk) {
	}

	Callback(void *environment, typename Base::Thunk function) : Base(environment, function) {
	}

	R operator()(Ts... args) const {
		return Base::getThunk()(Base::getEnvironment(), args...);
	}
};

namespace detail {
	template<class F>
	struct Arglist;

	template<class R, class Head, class... Ts>
	struct Arglist<R(Head, Ts...)> {
		using type = R(Head, Ts...);

		template <class Unshift>
		using unshift = Arglist<R(Unshift, Head, Ts...)>;

		using shift = Arglist<R(Ts...)>;
	};

	template<class R, class... Ts>
	struct Arglist<R(Ts...)> {
		using type = R(Ts...);

		template <class Unshift>
		using unshift = Arglist<R(Unshift, Ts...)>;
	};

	template<class F>
	using ArgShift = typename detail::Arglist<F>::shift::type;

	template<class F, class T>
	using ArgUnshift = typename detail::Arglist<F>::template unshift<T>::type;
}

template<typename Caller>
inline Callback<detail::ArgShift<get_func<Caller>>> makeCallback(const Caller &caller, get_argument<Caller, 0> callee) {
	return BindFirstOpaque<Caller>(callee);
}

template<class Caller, class F>
class CallerShiftFirst;

template<class Caller, class R, class FirstArgument, class... Ts>
class CallerShiftFirst<Caller, R(FirstArgument, Ts...)> {
public:
	using func = R(FirstArgument, Ts...);

	static R call(FirstArgument, Ts... args) {
		return Caller::call(args...);
	}
};

template<typename Caller>
inline Callback<get_func<Caller>> makeStatelessCallback(const Caller &caller) {
	return makeCallback(CallerShiftFirst<Caller, detail::ArgUnshift<get_func<Caller>, void *>>(), nullptr);
}

/// \brief Forms a Callback from a non-const Environment reference and a non-const Environment member-function.
template<class Environment, class F, MemberFunction<Environment, F> member>
using MemberCaller = BindFirstOpaque<Member<Environment, F, member>>;

/// \brief  Constructs a Callback1 from a non-const \p functor
///
/// \param Functor Must define \c first_argument_type and \c operator()(first_argument_type).
template<typename Functor>
inline Callback<get_func<Functor>> makeCallback(Functor &functor) {
	return MemberCaller<Functor, get_func<Functor>, &Functor::operator()>(functor);
}

/// \brief Forms a Callback from a const Environment reference and a const Environment member-function.
template<class Environment, class F, ConstMemberFunction<Environment, F> member>
using ConstMemberCaller = BindFirstOpaque<ConstMember<Environment, F, member>>;

/// \brief  Constructs a Callback1 from a const \p functor
///
/// \param Functor Must define \c first_argument_type and const \c operator()(first_argument_type).
template<typename Functor>
inline Callback<get_func<Functor>> makeCallback(const Functor &functor) {
	return ConstMemberCaller<Functor, get_func<Functor>, &Functor::operator()>(functor);
}

/// \brief Forms a Callback from a non-const Environment reference and a free function which operates on a non-const Environment reference.
template<class Environment, class F, detail::ArgUnshift<F, Environment &> *func>
using ReferenceCaller = BindFirstOpaque<Function<detail::ArgUnshift<F, Environment &>, func>>;

/// \brief Forms a Callback from a const Environment reference and a free function which operates on a const Environment reference.
template<class Environment, class F, detail::ArgUnshift<F, const Environment &> *func>
using ConstReferenceCaller = BindFirstOpaque<Function<detail::ArgUnshift<F, const Environment &>, func>>;

/// \brief Forms a Callback from a non-const Environment pointer and a free function which operates on a non-const Environment pointer.
template<class Environment, class F, detail::ArgUnshift<F, Environment *> *func>
using PointerCaller = BindFirstOpaque<Function<detail::ArgUnshift<F, Environment *>, func>>;

/// \brief Forms a Callback from a const Environment pointer and a free function which operates on a const Environment pointer.
template<class Environment, class F, detail::ArgUnshift<F, const Environment *> *func>
using ConstPointerCaller = BindFirstOpaque<Function<detail::ArgUnshift<F, const Environment *>, func>>;

namespace detail {
	template<class Caller, class F>
	class FreeCaller : public BindFirstOpaque<CallerShiftFirst<Caller, detail::ArgUnshift<F, void *>>> {
	public:
		FreeCaller() : BindFirstOpaque<CallerShiftFirst<Caller, detail::ArgUnshift<F, void *>>>(nullptr) {
		}
	};

	template<class F>
	struct FreeCallerWrapper;

	template<class R, class... Ts>
	struct FreeCallerWrapper<R(Ts...)> {
		using func = R(void *, Ts...);

		static R call(void *f, Ts... args) {
			// ideally, we'd get the implementation of the function type directly. Instead, it's passed in
			return reinterpret_cast<R(*)(Ts...)>(f)(args...);
		}
	};
}

/// \brief Forms a Callback from a free function
template<class F, F *func>
using FreeCaller = detail::FreeCaller<Function<F, func>, F>;

template<class R, class... Ts>
inline Callback<R(Ts...)> makeCallbackF(R(*func)(Ts...)) {
    void *pVoid = reinterpret_cast<void *>(func);
    return BindFirstOpaque<detail::FreeCallerWrapper<R(Ts...)>>(pVoid);
}

#endif