关于C ++：如何创建Boost phoenix make_shared？

how to create boost phoenix make_shared?

是否可以创建std::make_shared的Boost phoenix惰性变体？我的意思是，使像

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namespace p = boost::phoenix;
...
expr = custom_parser[_a=p::make_shared<Node>(_1,_2,_3)] >> ...

由于std::make_shared的可变模板性质，因此无法使用BOOST_PHOENIX_ADAPT_FUNCTION。因此，如果可能的话，包装器应该是可变参数模板本身。

如果可以保留额外的一组括号：

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namespace {
template <typename T>
struct make_shared_f
{
template <typename... A> struct result
{ typedef boost::shared_ptr< T > type; };

template <typename... A>
typename result<A...>::type operator()(A&&... a) const {
return boost::make_shared< T >(std::forward<A>(a)...);
}
};

template <typename T>
using make_shared_ = boost::phoenix::function<make_shared_f< T > >;
}

你可以使用像

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typedef std::vector<int> IntVec;
auto LazyInts = make_shared_<IntVec>()(arg1, arg2);

// create a shared vector of 7 ints '42'
auto ints = LazyInts(7, 42);
for (auto i : *ints) std::cout << i <<"";

在Coliru上实时观看

您的phx::make_shared与phx::construct非常相似。通过稍微更改construct的头文件，您可以获得：

在Coliru上运行

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//START OF PHOENIX_MAKE_SHARED.HPP

#ifndef BOOST_PHOENIX_MAKE_SHARED_HPP
#define BOOST_PHOENIX_MAKE_SHARED_HPP

#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>

#include <boost/phoenix/core/limits.hpp>
#include <boost/phoenix/core/call.hpp>
#include <boost/phoenix/core/expression.hpp>
#include <boost/phoenix/core/meta_grammar.hpp>
#include <boost/phoenix/object/detail/target.hpp>
#include <boost/phoenix/support/iterate.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
#include <boost/preprocessor/repetition/enum_shifted_binary_params.hpp>

BOOST_PHOENIX_DEFINE_EXPRESSION_VARARG(
(boost)(phoenix)(make_shared)
, (proto::terminal<detail::target<proto::_> >)
(meta_grammar)
, BOOST_PHOENIX_COMPOSITE_LIMIT
)

namespace boost { namespace phoenix
{
struct make_shared_eval
{
template <typename Sig>
struct result;

template <typename This, typename A0,typename Context>
struct result<This(A0, Context)>
{
typedef boost::shared_ptr<typename detail::result_of::target<A0>::type > type;
};

template <typename Target, typename Context>
typename boost::shared_ptr<typename detail::result_of::target<Target>::type>
operator()(Target, Context const &) const
{
return boost::make_shared<typename detail::result_of::target<Target>::type>();
}

#define EVAL_a(_,N,__) \\
BOOST_PP_COMMA_IF(BOOST_PP_DEC(N)) boost::phoenix::eval(a ## N, ctx)

#define GENERATE_MAKE_SHARED_EVAL(_,N,__) \\
template <typename This, BOOST_PHOENIX_typename_A(N), typename Context> \\
struct result<This(BOOST_PHOENIX_A(N), Context)> \\
{ \\
typedef boost::shared_ptr<typename detail::result_of::target<A0>::type > type; \\
}; \\
template <BOOST_PHOENIX_typename_A(N), typename Context> \\
typename boost::shared_ptr<typename detail::result_of::target<A0>::type > \\
operator()( \\
A0 const& \\
, BOOST_PP_ENUM_SHIFTED_BINARY_PARAMS( \\
N \\
, A \\
, const& a \\
) \\
, Context const & ctx \\
) const \\
{ \\
return \\
boost::make_shared<typename detail::result_of::target<A0>::type>( \\
BOOST_PP_REPEAT_FROM_TO( \\
1 \\
, N \\
, EVAL_a, _ \\
) \\
); \\
}

BOOST_PP_REPEAT_FROM_TO(2,BOOST_PHOENIX_COMPOSITE_LIMIT,GENERATE_MAKE_SHARED_EVAL,_)

#undef EVAL_a

#undef GENERATE_MAKE_SHARED_EVAL

};

template <typename Dummy>
struct default_actions::when<rule::make_shared, Dummy>
: call<make_shared_eval, Dummy>
{};

template <typename T>
inline
typename expression::make_shared<detail::target< T > >::type const
make_shared()
{
return
expression::
make_shared<detail::target< T > >::
make(detail::target< T >());
}

#define GENERATE_MAKE_SHARED(_,N,__) \\
template <typename T, BOOST_PHOENIX_typename_A(N)> \\
inline \\
typename expression::make_shared<detail::target< T >, BOOST_PHOENIX_A(N)>::type const \\
make_shared(BOOST_PHOENIX_A_const_ref_a(N)) \\
{ \\
return \\
expression:: \\
make_shared<detail::target< T >, BOOST_PHOENIX_A(N)>:: \\
make(detail::target< T >(), BOOST_PHOENIX_a(N)); \\
}

BOOST_PP_REPEAT_FROM_TO(1,BOOST_PHOENIX_COMPOSITE_LIMIT,GENERATE_MAKE_SHARED,_)

#undef GENERATE_MAKE_SHARED

}}

#endif

//END OF PHOENIX_MAKE_SHARED.HPP

#include <iostream>
#include <string>
#include <vector>

#define BOOST_SPIRIT_USE_PHOENIX_V3

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>

namespace phx=boost::phoenix;
namespace qi=boost::spirit::qi;

struct foo
{
foo():foo1(1),foo2(1.1){}
foo(int foo1_):foo1(foo1_),foo2(2.2){}
foo(int foo1_, double foo2_):foo1(foo1_),foo2(foo2_){}
int foo1;
double foo2;
};

int main()
{
//using phx::arg_names::arg1;
//using phx::arg_names::arg2;
//boost::shared_ptr<foo> var1 = phx::make_shared<foo>()();
//boost::shared_ptr<foo> var2 = phx::make_shared<foo>(arg1)(2);
//boost::shared_ptr<foo> var3 = phx::make_shared<foo>(arg1,arg2)(3,3.3);

//std::cout <<"var1:" << var1->foo1 <<"," << var1->foo2 << std::endl;
//std::cout <<"var2:" << var2->foo1 <<"," << var2->foo2 << std::endl;
//std::cout <<"var3:" << var3->foo1 <<"," << var3->foo2 << std::endl;

std::string test ="default,2,3-3.3";

qi::rule<std::string::const_iterator,boost::shared_ptr<foo>()> awful_rule =
qi::lit("default")[qi::_val=phx::make_shared<foo>()]
| (qi::int_ >> !qi::lit('-'))[qi::_val=phx::make_shared<foo>(qi::_1)]
| (qi::int_ >> qi::lit('-') >> qi::double_)[qi::_val=phx::make_shared<foo>(qi::_1,qi::_2)]
;
qi::rule<std::string::const_iterator,std::vector<boost::shared_ptr<foo> >()> parser = awful_rule%qi::lit(',');

std::string::const_iterator iter=test.begin(), end=test.end();

std::vector<boost::shared_ptr<foo> > foo_vector;
bool result = qi::parse(iter, end, parser, foo_vector);

if(result && (iter==end) )
{
std::cout <<"Success:" << std::endl;

for(std::size_t cont=0; cont < foo_vector.size(); ++cont)
std::cout << foo_vector[cont]->foo1 <<"," << foo_vector[cont]->foo2 << std::endl;
}
else
{
std::cout <<"Failure. Unparsed:" << std::string(iter,end) << std::endl;
}
}