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Thu, May 23, 05:17

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 {
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_t<head>::_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, int curr> struct get_at {
static_assert(pos >= 0, "Required parameter");
template <typename head, typename... tail>
static decltype(auto) get(head &&, tail &&... t) {
return get_at<pos, curr + 1>::get(std::forward<tail>(t)...);
}
};
template <int pos> struct get_at<pos, pos> {
static_assert(pos >= 0, "Required parameter");
template <typename head, typename... tail>
static decltype(auto) get(head && h, tail &&...) {
return std::forward<decltype(h._value)>(h._value);
}
};
// Optional version
template <int pos, int curr> struct get_optional {
template <typename T, typename... pack>
static decltype(auto) get(T &&, pack &&... _pack) {
return get_at<pos, curr>::get(std::forward<pack>(_pack)...);
}
};
template <int curr> struct get_optional<-1, curr> {
template <typename T, typename... pack>
static decltype(auto) get(T && _default, pack &&...) {
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) TAG_OF_ARGUMENT(_name)
#define REQUIRED_NAMED_ARG(_name) \
named_argument::get_at< \
named_argument::type_at<TAG_OF_ARGUMENT_WNS(_name), pack...>::_pos, \
0>::get(std::forward<pack>(_pack)...)
#define REQUIRED_NAMED_ARG(_name) \
named_argument::get_at< \
named_argument::type_at<TAG_OF_ARGUMENT_WNS(_name), pack...>::_pos, \
0>::get(std::forward<pack>(_pack)...)
#define OPTIONAL_NAMED_ARG(_name, _defaultVal) \
named_argument::get_optional< \
named_argument::type_at<TAG_OF_ARGUMENT_WNS(_name), pack...>::_pos, \
0>::get(_defaultVal, std::forward<pack>(_pack)...)
#define DECLARE_NAMED_ARGUMENT(name) \
struct TAG_OF_ARGUMENT(name) {}; \
named_argument::param_proxy<TAG_OF_ARGUMENT_WNS(name)> _##name \
__attribute__((unused))
namespace {
struct use_named_args_t {};
use_named_args_t use_named_args __attribute__((unused));
} // namespace
} // namespace akantu
#endif /* __AKANTU_AKA_NAMED_ARGUMENT_HH__ */

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