diff options
Diffstat (limited to 'indra/llcommon/apply.h')
| -rw-r--r-- | indra/llcommon/apply.h | 144 |
1 files changed, 130 insertions, 14 deletions
diff --git a/indra/llcommon/apply.h b/indra/llcommon/apply.h index 7c58d63bc0..cf6161ed50 100644 --- a/indra/llcommon/apply.h +++ b/indra/llcommon/apply.h @@ -12,8 +12,11 @@ #if ! defined(LL_APPLY_H) #define LL_APPLY_H +#include "llexception.h" #include <boost/type_traits/function_traits.hpp> +#include <functional> // std::mem_fn() #include <tuple> +#include <type_traits> // std::is_member_pointer namespace LL { @@ -54,20 +57,67 @@ namespace LL }, \ (ARGS)) -#if __cplusplus >= 201703L +/***************************************************************************** +* invoke() +*****************************************************************************/ +#if __cpp_lib_invoke >= 201411L // C++17 implementation -using std::apply; +using std::invoke; + +#else // no std::invoke + +// Use invoke() to handle pointer-to-method: +// derived from https://stackoverflow.com/a/38288251 +template<typename Fn, typename... Args, + typename std::enable_if<std::is_member_pointer<typename std::decay<Fn>::type>::value, + int>::type = 0 > +auto invoke(Fn&& f, Args&&... args) +{ + return std::mem_fn(std::forward<Fn>(f))(std::forward<Args>(args)...); +} + +template<typename Fn, typename... Args, + typename std::enable_if<!std::is_member_pointer<typename std::decay<Fn>::type>::value, + int>::type = 0 > +auto invoke(Fn&& f, Args&&... args) +{ + return std::forward<Fn>(f)(std::forward<Args>(args)...); +} + +#endif // no std::invoke + +/***************************************************************************** +* apply(function, tuple); apply(function, array) +*****************************************************************************/ +#if __cpp_lib_apply >= 201603L + +// C++17 implementation +// We don't just say 'using std::apply;' because that template is too general: +// it also picks up the apply(function, vector) case, which we want to handle +// below. +template <typename CALLABLE, typename... ARGS> +auto apply(CALLABLE&& func, const std::tuple<ARGS...>& args) +{ + return std::apply(std::forward<CALLABLE>(func), args); +} #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...>) +template <typename CALLABLE, typename... ARGS, std::size_t... I> +auto apply_impl(CALLABLE&& func, const std::tuple<ARGS...>& args, std::index_sequence<I...>) { + // We accept const std::tuple& so a caller can construct an tuple on the + // fly. But std::get<I>(const tuple) adds a const qualifier to everything + // it extracts. Get a non-const ref to this tuple so we can extract + // without the extraneous const. + auto& non_const_args{ const_cast<std::tuple<ARGS...>&>(args) }; + // call func(unpacked args) - return std::forward<CALLABLE>(func)(std::move(std::get<I>(args))...); + return invoke(std::forward<CALLABLE>(func), + std::forward<ARGS>(std::get<I>(non_const_args))...); } template <typename CALLABLE, typename... ARGS> @@ -81,6 +131,8 @@ auto apply(CALLABLE&& func, const std::tuple<ARGS...>& args) std::index_sequence_for<ARGS...>{}); } +#endif // C++14 + // per https://stackoverflow.com/a/57510428/5533635 template <typename CALLABLE, typename T, size_t SIZE> auto apply(CALLABLE&& func, const std::array<T, SIZE>& args) @@ -88,28 +140,92 @@ auto apply(CALLABLE&& func, const std::array<T, SIZE>& args) return apply(std::forward<CALLABLE>(func), std::tuple_cat(args)); } +/***************************************************************************** +* bind_front() +*****************************************************************************/ +// To invoke a non-static member function with a tuple, you need a callable +// that binds your member function with an instance pointer or reference. +// std::bind_front() is perfect: std::bind_front(&cls::method, instance). +// Unfortunately bind_front() only enters the standard library in C++20. +#if __cpp_lib_bind_front >= 201907L + +// C++20 implementation +using std::bind_front; + +#else // no std::bind_front() + +template<typename Fn, typename... Args, + typename std::enable_if<!std::is_member_pointer<typename std::decay<Fn>::type>::value, + int>::type = 0 > +auto bind_front(Fn&& f, Args&&... args) +{ + // Don't use perfect forwarding for f or args: we must bind them for later. + return [f, pfx_args=std::make_tuple(args...)] + (auto&&... sfx_args) + { + // Use perfect forwarding for sfx_args because we use them as soon as + // we receive them. + return apply( + f, + std::tuple_cat(pfx_args, + std::make_tuple(std::forward<decltype(sfx_args)>(sfx_args)...))); + }; +} + +template<typename Fn, typename... Args, + typename std::enable_if<std::is_member_pointer<typename std::decay<Fn>::type>::value, + int>::type = 0 > +auto bind_front(Fn&& f, Args&&... args) +{ + return bind_front(std::mem_fn(std::forward<Fn>(f)), std::forward<Args>(args)...); +} + +#endif // C++20 with std::bind_front() + +/***************************************************************************** +* apply(function, std::vector) +*****************************************************************************/ // per https://stackoverflow.com/a/28411055/5533635 template <typename CALLABLE, typename T, std::size_t... I> auto apply_impl(CALLABLE&& func, const std::vector<T>& args, std::index_sequence<I...>) { + return apply(std::forward<CALLABLE>(func), + std::make_tuple(args[I]...)); +} + +// produce suitable error if apply(func, vector) is the wrong size for func() +void apply_validate_size(size_t size, size_t arity); + +/// possible exception from apply() validation +struct apply_error: public LLException +{ + apply_error(const std::string& what): LLException(what) {} +}; + +template <size_t ARITY, typename CALLABLE, typename T> +auto apply_n(CALLABLE&& func, const std::vector<T>& args) +{ + apply_validate_size(args.size(), ARITY); return apply_impl(std::forward<CALLABLE>(func), - std::make_tuple(std::forward<T>(args[I])...), - I...); + args, + std::make_index_sequence<ARITY>()); } -// this goes beyond C++17 std::apply() +/** + * apply(function, std::vector) goes beyond C++17 std::apply(). For this case + * @a function @emph cannot be variadic: the compiler must know at compile + * time how many arguments to pass. This isn't Python. (But see apply_n() to + * pass a specific number of args to a variadic function.) + */ template <typename CALLABLE, typename T> auto apply(CALLABLE&& func, const std::vector<T>& args) { + // infer arity from the definition of func constexpr auto arity = boost::function_traits<CALLABLE>::arity; - assert(args.size() == arity); - return apply_impl(std::forward<CALLABLE>(func), - args, - std::make_index_sequence<arity>()); + // now that we have a compile-time arity, apply_n() works + return apply_n<arity>(std::forward<CALLABLE>(func), args); } -#endif // C++14 - } // namespace LL #endif /* ! defined(LL_APPLY_H) */ |