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/* Copyright (C) 2016 Murray Cumming
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3.0 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef SIGC_TUPLE_UTILS_TUPLE_TRANSFORM_EACH_H
#define SIGC_TUPLE_UTILS_TUPLE_TRANSFORM_EACH_H
#include <sigc++/tuple-utils/tuple_cdr.h>
#include <sigc++/tuple-utils/tuple_end.h>
#include <sigc++/tuple-utils/tuple_start.h>
#include <type_traits>
namespace sigc::internal
{
namespace detail
{
template<template<typename> class T_transformer, std::size_t size_from_index>
struct tuple_transform_each_impl
{
// TODO: Avoid the need to pass t_original all the way into the recursion?
template<typename T_current, typename T_original>
constexpr static decltype(auto) tuple_transform_each(T_current&& t, T_original& t_original)
{
if constexpr (size_from_index == 0)
{
// Prevent 'unreferenced formal parameter' warning from MSVC by 'using'
// t_original
static_cast<void>(t_original);
// Do nothing because the tuple has no elements.
return std::forward<T_current>(t);
}
else
{ // TODO: Should this compile without using else to contain the alternative code?
// We use std::decay_t<> because tuple_size is not defined for references.
constexpr auto size = std::tuple_size<std::decay_t<T_current>>::value;
constexpr auto index = size - size_from_index;
static_assert(index >= 0, "unexpected index.");
using from_element_type = typename std::tuple_element<index, std::decay_t<T_original>>::type;
using to_element_type =
typename std::invoke_result<decltype(&T_transformer<from_element_type>::transform),
from_element_type&>::type;
// Tuples which are input data to std::tuple_cat() should not be declared const.
// Some versions of libc++ has a bug in std::tuple_cat(): All output elements
// coming from a const tuple become const.
// https://github.com/libsigcplusplus/libsigcplusplus/issues/25
auto t_element = std::tuple<to_element_type>(
T_transformer<from_element_type>::transform(std::get<index>(t_original)));
if constexpr (size_from_index == 1)
{
auto tuple_rest = tuple_start<size - 1>(std::forward<T_current>(t));
return std::tuple_cat(tuple_rest, t_element);
}
else
{
auto t_start = tuple_start<index>(std::forward<T_current>(t));
// t_end's elements will be copies of the elements in t, so this method's
// caller won't see the changes made in the subsequent call of
// tuple_transform_each() on those copies. That's why we pass t_original
// through too, so we can modify that directly.
// the const version (tuple_transform_each_const()) doesn't have to worry
// about this, though avoiding copying would be more efficient.
auto t_end = tuple_end<size - index - 1>(t);
auto t_with_transformed_element = std::tuple_cat(t_start, t_element, t_end);
return tuple_transform_each_impl<T_transformer, size_from_index - 1>::tuple_transform_each(
t_with_transformed_element, t_original);
}
}
}
};
} // detail namespace
/**
* Get a tuple with each element having the transformed value of the element
* in the original tuple.
*/
template<template<typename> class T_transformer, typename T>
constexpr decltype(auto)
tuple_transform_each(T&& t)
{
// We use std::decay_t<> because tuple_size is not defined for references.
constexpr auto size = std::tuple_size<std::decay_t<T>>::value;
return detail::tuple_transform_each_impl<T_transformer, size>::tuple_transform_each(
std::forward<T>(t), t);
}
} // namespace sigc::internal
#endif // SIGC_TUPLE_UTILS_TUPLE_TRANSFORM_EACH_H
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