Hi Dave, Thanks for your reply. David Abrahams wrote:

David Abrahams writes:

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Edd Dawson writes:

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Hello all,

I have the following:

template<typename T> void f() { /* ... */ }

typedef boost::mpl::vector my_vec;

I'm looking for a way to call f<T>() for all types T in my_vec. I initially hoped that either an mpl algorithm or fusion::for_each might be able to accomplish this for me, but after reading through their docs this doesn't appear to be the case. struct call_f { template <class Wrapper> void operator()(Wrapper) Sorry, it's missing a "const" right here--^^^^ { f<typename Wrapper::type>(); } };

mpl::for_each >(call_f());

I didn't find this in the docs. Is it meant to be there? Unfortunately, that didn't quite work for me, anyway. A requirement of for_each (according to my MSVC 8 diagnostics) is that each type in the sequence must be default constructible. The (near) exact code I'm trying to compile is: struct register_cage { template<typename wrapper> void operator()(wrapper) const { // ... } }; struct null_type { }; // template template< BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_VECTOR_SIZE, typename T, null_type) > struct catch_exceptions { typedef typename boost::mpl::vector< BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_VECTOR_SIZE, T) >::type exception_types; catch_exceptions() { using namespace boost::mpl; typedef boost::mpl::_1 my1; typedef boost::mpl::_2 my2; // Remove all null_type entries and then sort the remaining ones, // most derived to front. typedef remove_if< exception_types, boost::is_same<_, null_type> >::type unique_exception_types; typedef sort< unique_exception_types, boost::is_base_of >::type sorted_exception_types; for_each >(register_cage()); } }; // Elsewhere, in 'client' code catch_exceptions(); The most appropriate part of the (long) compiler error is: 1>c:\development\boost\include\boost-1_33_1\boost\utility\value_init.hpp(34) : error C2512: 'std::runtime_error' : no appropriate default constructor available 1> c:\development\boost\include\boost-1_33_1\boost\utility\value_init.hpp(34) : while compiling class template member function 'boost::vinit_detail::non_const_T_base<T>::non_const_T_base(void)' Assuming that I have interpreted the compiler errors correctly, is this default-constructible requirement really necessary? I can do the task using the trick I listed in my original post so I would expect a library of this kind to be able to. Kind regards, Edd

David Abrahams wrote:

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struct call_f { template <class Wrapper> void operator()(Wrapper) Sorry, it's missing a "const" right here--^^^^ { f<typename Wrapper::type>(); } };

mpl::for_each >(call_f()); I didn't find this in the docs. Is it meant to be there?

The specific answer to your specific problem? No. Oh yeah, for_each wasn't documented in 1.33.1... and apparently it isn't documented in the CVS head either (still? Aleksey?)

Yep, I was referring to mpl::for_each in general.

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Unfortunately, that didn't quite work for me, anyway. A requirement of for_each (according to my MSVC 8 diagnostics) is that each type in the sequence must be default constructible.

In the case above, only mpl::identity<T> needs to be default-constructible for each type in the list... or that was my intention Ach! My mistake...

template <class T> struct make_identity { typedef mpl::identity<T> type; };

mpl::for_each >(call_f());

should work.

Like a charm! Many thanks! Kind Regards, Edd