58 lines
1.8 KiB
C++
58 lines
1.8 KiB
C++
|
/*!
|
||
|
|
@file
|
||
|
|
Defines `boost::hana::eval`.
|
||
|
|
|
||
|
|
@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_EVAL_HPP
|
||
|
|
#define BOOST_HANA_EVAL_HPP
|
||
|
|
|
||
|
|
#include <boost/hana/fwd/eval.hpp>
|
||
|
|
|
||
|
|
#include <boost/hana/config.hpp>
|
||
|
|
#include <boost/hana/core/dispatch.hpp>
|
||
|
|
#include <boost/hana/detail/wrong.hpp>
|
||
|
|
#include <boost/hana/functional/id.hpp>
|
||
|
|
|
||
|
|
|
||
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
||
|
|
//! @cond
|
||
|
|
template <typename Expr>
|
||
|
|
constexpr decltype(auto) eval_t::operator()(Expr&& expr) const {
|
||
|
|
return eval_impl<typename hana::tag_of<Expr>::type>::apply(
|
||
|
|
static_cast<Expr&&>(expr)
|
||
|
|
);
|
||
|
|
}
|
||
|
|
//! @endcond
|
||
|
|
|
||
|
|
template <typename T, bool condition>
|
||
|
|
struct eval_impl<T, when<condition>> : default_ {
|
||
|
|
template <typename Expr>
|
||
|
|
static constexpr auto eval_helper(Expr&& expr, int)
|
||
|
|
-> decltype(static_cast<Expr&&>(expr)())
|
||
|
|
{ return static_cast<Expr&&>(expr)(); }
|
||
|
|
|
||
|
|
template <typename Expr>
|
||
|
|
static constexpr auto eval_helper(Expr&& expr, long)
|
||
|
|
-> decltype(static_cast<Expr&&>(expr)(hana::id))
|
||
|
|
{ return static_cast<Expr&&>(expr)(hana::id); }
|
||
|
|
|
||
|
|
template <typename Expr>
|
||
|
|
static constexpr auto eval_helper(Expr&&, ...) {
|
||
|
|
static_assert(detail::wrong<Expr>{},
|
||
|
|
"hana::eval(expr) requires the expression to be a hana::lazy, "
|
||
|
|
"a nullary Callable or a unary Callable that may be "
|
||
|
|
"called with hana::id");
|
||
|
|
}
|
||
|
|
|
||
|
|
template <typename Expr>
|
||
|
|
static constexpr decltype(auto) apply(Expr&& expr)
|
||
|
|
{ return eval_helper(static_cast<Expr&&>(expr), int{}); }
|
||
|
|
};
|
||
|
|
BOOST_HANA_NAMESPACE_END
|
||
|
|
|
||
|
|
#endif // !BOOST_HANA_EVAL_HPP
|