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| -rw-r--r-- | indra/llcommon/apply.h | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/indra/llcommon/apply.h b/indra/llcommon/apply.h new file mode 100644 index 0000000000..ef4a8fd68b --- /dev/null +++ b/indra/llcommon/apply.h @@ -0,0 +1,51 @@ +/** + * @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) */ |