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aka_named_argument.hh
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/**
* @file aka_named_argument.hh
*
* @author Marco Arena
*
* @date creation Fri Jun 16 2017
*
* @brief A Documented file.
*
* @section LICENSE
*
* Public Domain ? https://gist.github.com/ilpropheta/7576dce4c3249df89f85
*
*/
/* -------------------------------------------------------------------------- */
#include <tuple>
#include <type_traits>
/* -------------------------------------------------------------------------- */
#ifndef __AKANTU_AKA_NAMED_ARGUMENT_HH__
#define __AKANTU_AKA_NAMED_ARGUMENT_HH__
namespace akantu {
struct use_named_args_t {};
extern use_named_args_t use_named_args;
namespace named_argument {
/* -- Pack utils (proxy version) --------------------------------------------
*/
/// Proxy containing [tag, value]
template <typename tag, typename type> struct param_t {
using _tag = tag;
using _type = type;
template <typename T>
explicit param_t(T && value) : _value(std::forward<T>(value)) {}
type _value;
};
/*
* Tagged proxy that allows syntax _name = value
* operator=(T&&) returns a param_t instance
**/
template <typename tag> struct param_proxy {
using _tag = tag;
template <typename T> decltype(auto) operator=(T && value) {
return param_t<tag, decltype(value)>{std::forward<T>(value)};
}
};
/* Same as type_at but it's supposed to be used by passing
a pack of param_t (_tag is looked for instead of a
plain type). This and type_at should be refactored.
*/
template <typename T, typename head, typename... tail> struct type_at_p {
enum {
_tmp = (std::is_same<T, typename std::decay<head>::type::_tag>::value)
? 0
: type_at_p<T, tail...>::_pos
};
enum { _pos = _tmp == -1 ? -1 : 1 + _tmp };
};
template <typename T, typename head> struct type_at_p<T, head> {
enum {
_pos =
(std::is_same<T, typename std::decay<head>::type::_tag>::value ? 1
: -1)
};
};
template <typename T, typename head, typename... tail> struct type_at {
enum { _tmp = type_at_p<T, head, tail...>::_pos };
enum { _pos = _tmp == 1 ? 0 : (_tmp == -1 ? -1 : _tmp - 1) };
};
/* Same as get_at but it's supposed to be used by passing
a pack of param_t (_type is retrieved instead)
This and get_at should be refactored.
*/
template <int pos, typename T> struct get_required {
static_assert(pos >= 0, " Missing required parameter, check the value of T "
"in get_required<pos, T>");
template <typename... types>
static decltype(auto) get(std::tuple<types &...> && t) {
return std::forward<decltype(std::get<pos>(t)._value)>(
std::get<pos>(t)._value);
}
};
// Optional version
template <int pos> struct get_optional {
template <typename T, typename... types>
static decltype(auto) get(T &&, std::tuple<types &...> && t) {
return get_required<pos, T>::get(std::forward<decltype(t)>(t));
}
};
template <> struct get_optional<-1> {
template <typename T, typename... types>
static decltype(auto) get(T && _default, std::tuple<types &...> &&) {
return std::forward<T>(_default);
}
};
} // namespace named_argument
// CONVENIENCE MACROS FOR CLASS DESIGNERS ==========
#define TAG_OF_ARGUMENT(name) p_##name
#define TAG_OF_ARGUMENT_WNS(name) named_argument::TAG_OF_ARGUMENT(name)
#define REQUIRED_NAMED_ARG(name) \
named_argument::get_required< \
named_argument::type_at<TAG_OF_ARGUMENT_WNS(name), pack...>::_pos, \
TAG_OF_ARGUMENT_WNS( \
name)>::get(std::forward_as_tuple<pack...>(_pack...))
#define OPTIONAL_NAMED_ARG(name, _defaultVal) \
named_argument::get_optional< \
named_argument::type_at<TAG_OF_ARGUMENT_WNS(name), pack...>::_pos>:: \
get(_defaultVal, std::forward_as_tuple<pack...>(_pack...))
#define DECLARE_NAMED_ARGUMENT(name) \
namespace named_argument { \
struct TAG_OF_ARGUMENT(name) {}; \
} \
extern named_argument::param_proxy<TAG_OF_ARGUMENT_WNS(name)> _##name
#define CREATE_NAMED_ARGUMENT(name) \
named_argument::param_proxy<TAG_OF_ARGUMENT_WNS(name)> _##name
// FULL EXAMPLE ====================================
// step 1) generate tags you need
// namespace {
// CREATE_TAG(title);
// CREATE_TAG(h);
// CREATE_TAG(w);
// CREATE_TAG(posx);
// CREATE_TAG(posy);
// CREATE_TAG(handle);
// } // namespace
// // step 2) use tags/proxies in your class
// class window {
// public:
// // classic constructor
// window(string pTitle, int pH, int pW, int pPosx, int pPosy, int &
// pHandle)
// : title(move(pTitle)), h(pH), w(pW), posx(pPosx), posy(pPosy),
// handle(pHandle) {}
// // constructor using proxies (e.g. _title = "title")
// template <typename... pack>
// window(use_named_t, pack &&... _pack)
// : window{REQUIRED_NAME(title), // required
// OPTIONAL_NAME(h, 100), // optional
// OPTIONAL_NAME(w, 400), // optional
// OPTIONAL_NAME(posx, 0), // optional
// OPTIONAL_NAME(posy, 0), // optional
// REQUIRED_NAME(handle)} // required
// {}
// // constructor using tags (e.g. __title, "title")
// template <typename... pack>
// window(use_tags_t, pack &&... _pack)
// : window{REQUIRED_TAG(title), // required
// OPTIONAL_TAG(h, 100), // optional
// OPTIONAL_TAG(w, 400), // optional
// OPTIONAL_TAG(posx, 0), // optional
// OPTIONAL_TAG(posy, 0), // optional
// REQUIRED_TAG(handle)} // required
// {}
// friend ostream & operator<<(ostream & os, const window &);
// private:
// string title;
// int h, w;
// int posx, posy;
// int & handle;
// };
// ostream & operator<<(ostream & os, const window & w) {
// os << "WINDOW: " << w.title << " (" << w.h << "x" << w.w << "), at " <<
// w.posx
// << "," << w.posy << "->" << w.handle;
// return os;
// }
// int main() {
// int i = 5;
// {
// window w{use_tags, __title, "Title", __h, 10, __w, 100, __handle, i};
// cout << w << endl;
// }
// {
// window w{use_named, _h = 10, _title = "Title", _handle = i, _w = 100};
// cout << w << endl;
// }
// {
// window w{"Title", 10, 400, 0, 0, i};
// cout << w << endl;
// }
// }
} // namespace akantu
#endif /* __AKANTU_AKA_NAMED_ARGUMENT_HH__ */

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