将Boost参数与运算符()一起使用

Question

我想将Boost Parameter与重载调用运算符(operator()(一起使用：

#include <string>
#include <boost/parameter/keyword.hpp>
#include <boost/parameter/preprocessor.hpp>
struct add_argument_tag
{
struct name_;
struct descr_;
};
static inline boost::parameter::keyword<add_argument_tag::name_>&  name  = boost::parameter::keyword<add_argument_tag::name_>::get();
static inline boost::parameter::keyword<add_argument_tag::descr_>& descr = boost::parameter::keyword<add_argument_tag::descr_>::get();
struct config
{
BOOST_PARAMETER_MEMBER_FUNCTION(
(config),
operator(),
add_argument_tag,
(required (name_, (std::string const&)))
(optional
(descr_, (std::string const&), "")
)
)
{
return *this;
}
};
int main()
{
config my_config;
my_config
("foo")
("bar", descr = "some description");
}

不幸的是，它不起作用：

In file included from /usr/include/boost/mpl/aux_/integral_wrapper.hpp:22,
from /usr/include/boost/mpl/int.hpp:20,
from /usr/include/boost/mpl/lambda_fwd.hpp:23,
from /usr/include/boost/mpl/aux_/na_spec.hpp:18,
from /usr/include/boost/mpl/identity.hpp:17,
from /usr/include/boost/parameter/aux_/unwrap_cv_reference.hpp:11,
from /usr/include/boost/parameter/keyword.hpp:9,
from /.../main.cpp:2:
/.../main.cpp:18:18: error: expected unqualified-id before ')' token
operator(),
^
/.../main.cpp:18:18: error: expected unqualified-id before ')' token
operator(),
^
/.../main.cpp:18:18: error: expected unqualified-id before ')' token
operator(),
^
/.../main.cpp:16:5: error: expected nested-name-specifier before 'boost_param_result_24operator'
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /.../main.cpp:3:
/.../main.cpp:16:5: error: expected initializer before '<' token
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/boost/mpl/aux_/integral_wrapper.hpp:22,
from /usr/include/boost/mpl/int.hpp:20,
from /usr/include/boost/mpl/lambda_fwd.hpp:23,
from /usr/include/boost/mpl/aux_/na_spec.hpp:18,
from /usr/include/boost/mpl/identity.hpp:17,
from /usr/include/boost/parameter/aux_/unwrap_cv_reference.hpp:11,
from /usr/include/boost/parameter/keyword.hpp:9,
from /.../main.cpp:2:
/.../main.cpp:16:5: error: expected nested-name-specifier before 'boost_param_result_24operator'
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /.../main.cpp:3:
/.../main.cpp:16:5: error: expected initializer before '<' token
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../main.cpp:16:5: error: 'boost_param_default_24operator' declared as function returning a function
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../main.cpp:16:5: error: 'boost_param_default_24operator' declared as function returning a function
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/boost/mpl/aux_/integral_wrapper.hpp:22,
from /usr/include/boost/mpl/int.hpp:20,
from /usr/include/boost/mpl/lambda_fwd.hpp:23,
from /usr/include/boost/mpl/aux_/na_spec.hpp:18,
from /usr/include/boost/mpl/identity.hpp:17,
from /usr/include/boost/parameter/aux_/unwrap_cv_reference.hpp:11,
from /usr/include/boost/parameter/keyword.hpp:9,
from /.../main.cpp:2:
/.../main.cpp:16:5: error: expected nested-name-specifier before 'boost_param_result_24operator'
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /.../main.cpp:3:
/.../main.cpp:16:5: error: expected initializer before '<' token
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../main.cpp:16:5: error: 'boost_param_default_24operator' declared as function returning a function
BOOST_PARAMETER_MEMBER_FUNCTION(
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../main.cpp: In function 'int main()':
/.../main.cpp:34:15: error: no match for call to '(config) (const char [4])'
("foo")
^
make[3]: *** [CMakeFiles/BoostParameterProblem.dir/build.make:63: CMakeFiles/BoostParameterProblem.dir/main.cpp.o] Error 1
make[2]: *** [CMakeFiles/Makefile2:73: CMakeFiles/BoostParameterProblem.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:85: CMakeFiles/BoostParameterProblem.dir/rule] Error 2
make: *** [Makefile:118: BoostParameterProblem] Error 2

通过使用一个适当命名的函数而不是operator()，我可以很容易地解决这个问题，但我真的很想在这里使用operator()…：(

我猜原因是Boost Parameter如何使用宏和元编程来构建辅助函数等，而使用运算符重载函数根本不可能。

有人做过这样的作品吗？这可能吗？

Answer 1

Boost Parameter确实做了很多字符串连接的事情，因此您的operator()将被连接到一个无效的名称。

解决方法之一是将operator()委派给它的实现。更改宏部分以定义一个正常函数，然后完美地转发所有参数和最终结果：

struct config
{
BOOST_PARAMETER_MEMBER_FUNCTION(
(config),
myope,
add_argument_tag,
(required (name_, (std::string const&)))
(optional
(descr_, (std::string const&), "")
)
)
{
std::cout << name_ << " " << descr_ << "n";
return *this;
}
template<class... Args>
decltype(auto) operator() (Args&& ...args) {
return myope(std::forward<Args>(args)...);
}
};

实时演示