Edit: /usr/include/boost/hana/while.hpp (4441B)
/*!
@file
Defines `boost::hana::while_`.
@copyright Louis Dionne 2013-2017
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_WHILE_HPP
#define BOOST_HANA_WHILE_HPP
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template
constexpr decltype(auto) while_t::operator()(Pred&& pred, State&& state, F&& f) const {
using Cond = decltype(pred(state));
using Bool = typename hana::tag_of::type;
using While = BOOST_HANA_DISPATCH_IF(while_impl,
hana::Logical::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Logical::value,
"hana::while_(pred, state, f) requires 'pred(state)' to be a Logical");
#endif
return While::apply(static_cast(pred),
static_cast(state),
static_cast(f));
}
//! @endcond
template
struct while_impl> : hana::default_ {
template
static constexpr auto apply(Args&& ...) = delete;
};
template
struct while_impl::value>> {
template
static auto apply(Pred&& pred, State&& state, F&& f)
-> decltype(
true ? f(static_cast(state))
: static_cast(state)
)
{
if (pred(state)) {
decltype(auto) r = f(static_cast(state));
return hana::while_(static_cast(pred),
static_cast(r),
static_cast(f));
}
else {
return static_cast(state);
}
}
};
template
struct while_impl::value &&
hana::Logical::value
>> {
template
static constexpr State
while_helper(hana::false_, Pred&&, State&& state, F&&) {
return static_cast(state);
}
template
static constexpr decltype(auto)
while_helper(hana::true_, Pred&& pred, State&& state, F&& f) {
decltype(auto) r = f(static_cast(state));
return hana::while_(static_cast(pred),
static_cast(r),
static_cast(f));
}
template
static constexpr decltype(auto)
apply(Pred&& pred, State&& state, F&& f) {
// Since `pred(state)` returns a `Constant`, we do not actually
// need to call it; we only need its decltype. However, we still
// call it to run potential side effects. I'm not sure whether
// that is desirable, since we pretty much take for granted that
// functions are pure, but we'll do it like this for now. Also, I
// think there is something rather deep hidden behind this, and
// understanding what must be done here should give us a better
// understanding of something non-trivial.
auto cond_ = pred(state);
constexpr auto cond = hana::value(cond_);
constexpr bool truth_value = hana::if_(cond, true, false);
return while_helper(hana::bool_c,
static_cast(pred),
static_cast(state),
static_cast(f));
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_WHILE_HPP