auto scope_value = 123;
cout << "NEW demo:" << endl;
auto xs = fusion::make_vector
(
NEW((y, 0.5)(x, scope_value + 1)),
NEW((x, 0.05)(y, 10)(p, 0.001))
);
fusion::for_each(xs, [](auto x)
{
cout << "x.x = " << x.x << ", sizeof(x) = " << sizeof(x) << endl;
});
cout << endl << "NEW_LAZY demo:" << endl;
fusion::for_each(transform(xs, NEW_LAZY((y, scope_value + 11)(q, _1))), [](auto x)
{
cout << "x.q.x = " << x.q.x << ", sizeof(x) = " << sizeof(x) << endl;
});
Output:
NEW demo:
x.x = 124, sizeof(x) = 16
x.x = 0.05, sizeof(x) = 24
NEW_LAZY demo:
x.q.x = 124, sizeof(x) = 24
x.q.x = 0.05, sizeof(x) = 32
LIVE DEMO
| | code |
| | // Copyright Evgeny Panasyuk 2014.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
// e-mail: E?????[dot]P???????[at]gmail.???
// Emulation of "Anonymous Types"
// GOTO main
#include <boost/preprocessor/punctuation/comma_if.hpp>
#include <boost/preprocessor/seq/for_each_i.hpp>
#include <boost/preprocessor/seq/pop_front.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
#include <boost/preprocessor/seq/elem.hpp>
#include <boost/preprocessor/tuple/elem.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/fusion/container.hpp>
#include <boost/fusion/algorithm.hpp>
#include <boost/phoenix/phoenix.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/mpl/at.hpp>
#include <iostream>
#include <utility>
/************************************************************************************************/
// refer http://www.boost.org/doc/libs/1_56_0/boost/fusion/adapted/struct/define_struct.hpp
// rerquired for sequence of tuples syntax ((a,b)(c,d)...)
#define ANONYMOUS_TYPE_0(X, Y) ((X, Y)) ANONYMOUS_TYPE_1
#define ANONYMOUS_TYPE_1(X, Y) ((X, Y)) ANONYMOUS_TYPE_0
#define ANONYMOUS_TYPE_0_END
#define ANONYMOUS_TYPE_1_END
#define VAR_NAME(elem) BOOST_PP_TUPLE_ELEM(2, 0, elem)
#define VAR_VALUE(elem) BOOST_PP_TUPLE_ELEM(2, 1, elem)
#define VALUES(r, data, i, elem) BOOST_PP_COMMA_IF(i) VAR_VALUE(elem)
#define DECLARE_MEMBER(r, data, i, elem) typename boost::mpl::at_c<Ts, i>::type VAR_NAME(elem);
#define FOR_EACH_DECL(action, seq) \
BOOST_PP_SEQ_FOR_EACH_I(action, _, BOOST_PP_SEQ_POP_FRONT(BOOST_PP_CAT(ANONYMOUS_TYPE_0(0,0)seq,_END))) \
/**/
#define NEW_AUX(seq) \
[](auto... args) \
{ \
using Ts = boost::mpl::vector<decltype(args)...>; \
struct \
{ \
FOR_EACH_DECL(DECLARE_MEMBER, seq)\
} anonymous = {std::move(args)...}; \
return anonymous; \
} \
/**/
#define NEW_LAZY(seq) (boost::phoenix::bind(NEW_AUX(seq), FOR_EACH_DECL(VALUES, seq)))
#define NEW(seq) (NEW_AUX(seq)(FOR_EACH_DECL(VALUES, seq)))
/************************************************************************************************/
int main()
{
using namespace std;
using namespace boost;
using phoenix::arg_names::_1;
auto scope_value = 123;
cout << "NEW demo:" << endl;
auto xs = fusion::make_vector
(
NEW((y, 0.5)(x, scope_value + 1)),
NEW((x, 0.05)(y, 10)(p, 0.001))
);
fusion::for_each(xs, [](auto x)
{
cout << "x.x = " << x.x << ", sizeof(x) = " << sizeof(x) << endl;
});
cout << endl << "NEW_LAZY demo:" << endl;
fusion::for_each(transform(xs, NEW_LAZY((y, scope_value + 11)(q, _1))), [](auto x)
{
cout << "x.q.x = " << x.q.x << ", sizeof(x) = " << sizeof(x) << endl;
});
}
|
| | |
NEW_LAZY можно сделать на основе лямбд, без bind'а — тогда не будет bind expression, зато будет работать member access у аргументов.
Думаю при желании/необходимости можно адаптировать структуру к Boost.Fusion через CRTP (что-то наподобие BOOST_FUSION_DEFINE_STRUCT_INLINE).
Где применимо не знаю. Если такое потребуется — можно и лямбду вручную расписать.
Встретилось нечто подобное при решении одной задачки. Оставляю здесь — может кому пригодится / на какие мысли наведёт.
P.S. Эта реализация для C++14. В первом же варианте реализация была C++11, но без LAZY:
| | first version |
| | http://coliru.stacked-crooked.com/a/d38afecc3a2a893c
// Copyright Evgeny Panasyuk 2014.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
// e-mail: E?????[dot]P???????[at]gmail.???
// Emulation of "Anonymous Types"
// GOTO main
#include <boost/preprocessor/seq/pop_front.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
#include <boost/preprocessor/seq/elem.hpp>
#include <boost/preprocessor/tuple/elem.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/fusion/container.hpp>
#include <boost/fusion/algorithm.hpp>
#include <iostream>
#include <utility>
using namespace std;
using namespace boost;
using namespace fusion;
// refer http://www.boost.org/doc/libs/1_56_0/boost/fusion/adapted/struct/define_struct.hpp
#define ANONYMOUS_TYPE_0(X, Y) ((X, Y)) ANONYMOUS_TYPE_1
#define ANONYMOUS_TYPE_1(X, Y) ((X, Y)) ANONYMOUS_TYPE_0
#define ANONYMOUS_TYPE_0_END
#define ANONYMOUS_TYPE_1_END
#define VAR_NAME(elem) BOOST_PP_TUPLE_ELEM(2, 0, elem)
#define VAR_VALUE(elem) BOOST_PP_TUPLE_ELEM(2, 1, elem)
#define MOVE_VAR(r, data, elem) std::move(BOOST_PP_CAT(VAR_NAME(elem), __aux)),
#define DECLARE_VAR(r, data, elem) auto BOOST_PP_CAT(VAR_NAME(elem), __aux) = VAR_VALUE(elem);
#define DECLARE_MEMBER(r, data, elem) decltype(BOOST_PP_CAT(VAR_NAME(elem), __aux)) VAR_NAME(elem);
#define FOR_EACH_DECL(action, seq) \
BOOST_PP_SEQ_FOR_EACH(action, _, BOOST_PP_SEQ_POP_FRONT(BOOST_PP_CAT(ANONYMOUS_TYPE_0(0,0)seq,_END))) \
/**/
#define NEW(seq) \
[&] \
{ \
FOR_EACH_DECL(DECLARE_VAR, seq)\
struct \
{ \
FOR_EACH_DECL(DECLARE_MEMBER, seq)\
} anonymous = {FOR_EACH_DECL(MOVE_VAR, seq)}; \
return anonymous; \
}() \
/**/
int main()
{
auto scope_value = 123;
auto xs = make_vector
(
NEW((y, 0.5)(x, scope_value + 1)),
NEW((x, 0.05)(y, 10)(p,0.001))
);
for_each(xs, [](auto x)
{
cout << "x.x = " << x.x << ", sizeof(x) = " << sizeof(x) << endl;
});
}
|
| | |
