boost/flyweight/detail/perfect_fwd.hpp

/* Copyright 2006-2014 Joaquin M Lopez Munoz.
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 *
 * See http://www.boost.org/libs/flyweight for library home page.
 */

#ifndef BOOST_FLYWEIGHT_DETAIL_PERFECT_FWD_HPP
#define BOOST_FLYWEIGHT_DETAIL_PERFECT_FWD_HPP

#if defined(_MSC_VER)
#pragma once
#endif

/* C++03-compatible implementation of perfect forwarding.
 * Usage:
 *
 *  # define NAME ...
 *  # define BODY(args) {...BOOST_FLYWEIGHT_FORWARD(args)...}
 *  BOOST_FLYWEIGHT_PERFECT_FWD(name,body)
 *
 * where NAME includes the return type and qualifiers (if any) and BODY(args)
 * is expected to fo the forwarding through BOOST_FLYWEIGHT_FORWARD(args).
 *
 * In compilers capable of perfect forwarding, the real thing is provided
 * (just one variadic args overload is generated). Otherwise the machinery
 * generates n+1 overloads, if rvalue refs are supported, or else 2^(n+1)-1
 * overloads accepting any combination of lvalue refs and const lvalue refs,
 * up to BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS args.
 *
 * BOOST_FLYWEIGHT_PERFECT_FWD_WITH_ARGS(name,body) is a variation omitting the
 * overloads with zero args --when perfect forwarding is available, this second
 * macro is exactly the same as the original. 
 */

#include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/repetition/enum.hpp>
#include <boost/preprocessor/repetition/enum_params.hpp>
#include <boost/preprocessor/seq/seq.hpp>

#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#include <utility>
#endif

#define BOOST_FLYWEIGHT_FORWARD_FORWARD_AUX(z,n,_) \
std::forward<BOOST_PP_CAT(T,n)>(BOOST_PP_CAT(t,n))

#define BOOST_FLYWEIGHT_FORWARD_FORWARD(n) \
BOOST_PP_ENUM(n,BOOST_FLYWEIGHT_FORWARD_FORWARD_AUX,~)

#define BOOST_FLYWEIGHT_FORWARD_ENUM(n) BOOST_PP_ENUM_PARAMS(n,t)

#define BOOST_FLYWEIGHT_FORWARD_PASS(arg) arg

#define BOOST_FLYWEIGHT_FORWARD(args)\
BOOST_PP_CAT(BOOST_FLYWEIGHT_FORWARD_,BOOST_PP_SEQ_HEAD(args))( \
BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_TAIL(args)))

#if defined(BOOST_NO_CXX11_RVALUE_REFERENCES)||\
    defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)

#if !defined(BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS)
#define BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS 5
#endif

#if BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS<0
#error BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS must be >=0
#endif

#if BOOST_FLYWEIGHT_LIMIT_PERFECT_FWD_ARGS<=5
#include <boost/flyweight/detail/pp_perfect_fwd.hpp>
#else
#include <boost/flyweight/detail/dyn_perfect_fwd.hpp>
#endif

#else

/* real perfect forwarding */

#define BOOST_FLYWEIGHT_PERFECT_FWD(name,body) \
template<typename... Args>name(Args&&... args) \
body((PASS)(std::forward<Args>(args)...))

#define BOOST_FLYWEIGHT_PERFECT_FWD_WITH_ARGS  \
BOOST_FLYWEIGHT_PERFECT_FWD

#endif
#endif
Boost C++ Libraries

boost/flyweight/detail/perfect_fwd.hpp
