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/*!
@file
Defines `boost::hana::overload_linearly`.
@copyright Louis Dionne 2013-2016
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_FUNCTIONAL_OVERLOAD_LINEARLY_HPP
#define BOOST_HANA_FUNCTIONAL_OVERLOAD_LINEARLY_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/detail/decay.hpp>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN
//! @ingroup group-functional
//! Call the first function that produces a valid call expression.
//!
//! Given functions `f1, ..., fn`, `overload_linearly(f1, ..., fn)` is
//! a new function that calls the first `fk` producing a valid call
//! expression with the given arguments. Specifically,
//! @code
//! overload_linearly(f1, ..., fn)(args...) == fk(args...)
//! @endcode
//!
//! where `fk` is the _first_ function such that `fk(args...)` is a valid
//! expression.
//!
//!
//! Example
//! -------
//! @include example/functional/overload_linearly.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto overload_linearly = [](auto&& f1, auto&& f2, ..., auto&& fn) {
return [perfect-capture](auto&& ...x) -> decltype(auto) {
return forwarded(fk)(forwarded(x)...);
};
};
#else
template <typename F, typename G>
struct overload_linearly_t {
F f;
G g;
private:
template <typename ...Args, typename =
decltype(std::declval<F const&>()(std::declval<Args>()...))>
constexpr F const& which(int) const& { return f; }
template <typename ...Args, typename =
decltype(std::declval<F&>()(std::declval<Args>()...))>
constexpr F& which(int) & { return f; }
template <typename ...Args, typename =
decltype(std::declval<F&&>()(std::declval<Args>()...))>
constexpr F which(int) && { return static_cast<F&&>(f); }
template <typename ...Args>
constexpr G const& which(long) const& { return g; }
template <typename ...Args>
constexpr G& which(long) & { return g; }
template <typename ...Args>
constexpr G which(long) && { return static_cast<G&&>(g); }
public:
template <typename ...Args>
constexpr decltype(auto) operator()(Args&& ...args) const&
{ return which<Args...>(int{})(static_cast<Args&&>(args)...); }
template <typename ...Args>
constexpr decltype(auto) operator()(Args&& ...args) &
{ return which<Args...>(int{})(static_cast<Args&&>(args)...); }
template <typename ...Args>
constexpr decltype(auto) operator()(Args&& ...args) &&
{ return which<Args...>(int{})(static_cast<Args&&>(args)...); }
};
struct make_overload_linearly_t {
template <typename F, typename G>
constexpr overload_linearly_t<
typename detail::decay<F>::type,
typename detail::decay<G>::type
> operator()(F&& f, G&& g) const {
return {static_cast<F&&>(f), static_cast<G&&>(g)};
}
template <typename F, typename G, typename ...H>
constexpr decltype(auto) operator()(F&& f, G&& g, H&& ...h) const {
return (*this)(static_cast<F&&>(f),
(*this)(static_cast<G&&>(g), static_cast<H&&>(h)...));
}
template <typename F>
constexpr typename detail::decay<F>::type operator()(F&& f) const {
return static_cast<F&&>(f);
}
};
constexpr make_overload_linearly_t overload_linearly{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FUNCTIONAL_OVERLOAD_LINEARLY_HPP
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