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/**
* @file apply.h
* @author Nat Goodspeed
* @date 2022-06-18
* @brief C++14 version of std::apply()
*
* $LicenseInfo:firstyear=2022&license=viewerlgpl$
* Copyright (c) 2022, Linden Research, Inc.
* $/LicenseInfo$
*/
#if ! defined(LL_APPLY_H)
#define LL_APPLY_H
#include <tuple>
namespace LL
{
#if __cplusplus >= 201703L
// C++17 implementation
using std::apply;
#else // C++14
// Derived from https://stackoverflow.com/a/20441189
// and https://en.cppreference.com/w/cpp/utility/apply
template <typename CALLABLE, typename TUPLE, std::size_t... I>
auto apply_impl(CALLABLE&& func, TUPLE&& args, std::index_sequence<I...>)
{
// call func(unpacked args)
return std::forward<CALLABLE>(func)(std::move(std::get<I>(args))...);
}
template <typename CALLABLE, typename... ARGS>
auto apply(CALLABLE&& func, std::tuple<ARGS...>&& args)
{
// std::index_sequence_for is the magic sauce here, generating an argument
// pack of indexes for each entry in args. apply_impl() can then pass
// those to std::get() to unpack args into individual arguments.
return apply_impl(std::forward<CALLABLE>(func),
std::forward<std::tuple<ARGS...>>(args),
std::index_sequence_for<ARGS...>{});
}
#endif // C++14
} // namespace LL
#endif /* ! defined(LL_APPLY_H) */
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