third_party/boost/parameter/test/literate/extracting-parameter-types0.cpp

#include <boost/parameter.hpp>

BOOST_PARAMETER_NAME(name)
BOOST_PARAMETER_NAME(index)

template <typename T>
#if defined(BOOST_PARAMETER_HAS_PERFECT_FORWARDING)
void noop(T&&)
#else
void noop(T&)
#endif
{
}

#if defined(BOOST_PARAMETER_HAS_PERFECT_FORWARDING)
#include <utility>
#endif

template <typename Name, typename Index>
#if defined(BOOST_PARAMETER_HAS_PERFECT_FORWARDING)
int deduce_arg_types_impl(Name&& name, Index&& index)
{
    noop(std::forward<Name>(name));
    noop(std::forward<Index>(index));
    return index;
}
#else
int deduce_arg_types_impl(Name& name, Index& index)
{
    Name& n2 = name;  // we know the types
    Index& i2 = index;
    noop(n2);
    noop(i2);
    return index;
}
#endif

template <typename ArgumentPack>
int deduce_arg_types(ArgumentPack const& args)
{
    return deduce_arg_types_impl(args[_name], args[_index|42]);
}

#include <boost/core/lightweight_test.hpp>

int main()
{
    int a1 = deduce_arg_types((_name = "foo"));
    int a2 = deduce_arg_types((_name = "foo", _index = 3));
    BOOST_TEST_EQ(a1, 42);
    BOOST_TEST_EQ(a2, 3);
    return boost::report_errors();
}