John Maddock wrote:
From within the body of the BOOST_PARAMETER_FUNCTION generated
function it
appears that I can use the name "Args" to refer to the type of the
argument pack, and maybe in the return type as well? But this isn't
documented, so can I rely on it?
Apparently not, some more experimentation suggests that "Args" can't be
easily used to compute the return type; if I use:
typename compute_result<Args>::type
as the return type of the function in BOOST_PARAMETER_FUNCTION, then
everything is OK, provided I don't try and actually extract anything from
the type Args inside compute_result, but if I define it as:
template <class Args>
struct compute_result
{
typedef typename boost::parameter::value_type<
Args, tag::domain_error, throw_on_error_type>
::type type;
};
Then I get endless compiler errors starting with:
c:\data\boost\release\boost\boost\parameter\value_type.hpp(62) : error
C2661: 'boost::mpl::assert_not_arg' : no overloaded function takes 2
arguments
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(83) : see
reference to class template instantiation
'boost::parameter::value_type' being compiled
with
[
Parameters=boost::mpl::pairboost::parameter::aux::empty_arg_list,boost::parameter::void_,
Keyword=tag::domain_error,
Default=throw_on_error_type
]
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) : see
reference to class template instantiation 'compute_result<Args>' being
compiled
with
[
Args=boost::mpl::pairboost::parameter::aux::empty_arg_list,boost::parameter::void_
]
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) : see
reference to class template instantiation
'boost_param_result_101policy<Args>' being compiled
with
[
Args=boost::mpl::pairboost::parameter::aux::empty_arg_list,boost::parameter::void_
]
c:\data\boost\release\boost\boost\parameter\value_type.hpp(62) : error
C2866:
'boost::parameter::value_type::mpl_assertion_in_line_67'
: a const static data member of a managed type must be initialized at the
point of declaration
with
[
Parameters=boost::mpl::pairboost::parameter::aux::empty_arg_list,boost::parameter::void_,
Keyword=tag::domain_error,
Default=throw_on_error_type
]
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) :
error C2146: syntax error : missing ';' before identifier 'type'
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) :
error C3254: 'boost_param_result_101policy<Args>' : class contains explicit
override 'type' but does not derive from an interface that contains the
function declaration
with
[
Args=boost::mpl::pairboost::parameter::aux::empty_arg_list,boost::parameter::void_
]
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) :
error C2838: 'type' : illegal qualified name in member declaration
c:\data\boost\boost\sandbox\math_toolkit\libs\math\ide\scrap.cpp(101) :
error C4430: missing type specifier - int assumed. Note: C++ does not
support default-int
Obviously it's not easy to figure out what's going on here, given that this
happens inside a macro expansion :-(
Thanks for any insight, John.
