On Sat, Feb 12, 2011 at 1:34 PM, Lorenzo Caminiti <lorcaminiti@gmail.com> wrote:

On Sun, Feb 6, 2011 at 2:25 PM, Mathias Gaunard <mathias.gaunard@ens-lyon.org> wrote:

...

As I said, it does. With Boost.Local, you can still call polymorphic functions on the variables captured from scope without specifying the types of the arguments.

I am thinking to provide the type of the bound parameters within the local function body as `<BOUND_PARAM_NAME>_type`. This way you can use such types to check concepts, etc...

Is there value in this?

#include <boost/local/function.hpp> #include <boost/concept_check.hpp> #include <iostream>

template<typename T> class Addable {    T x;    T y;    void return_type(T); // Used to check addition returns type `T`. public:    BOOST_CONCEPT_USAGE(Addable) {        return_type(x + y); // Check addition `T operator+(T x, T y)`.    } };

struct pod {};

int main() {    pod sum; // Can't be added.    int factor = 10;

   BOOST_LOCAL_FUNCTION(    (void) (add)( (double)(num) (const bind)((factor)) (bind)((&sum)) )    ) {        // In here `sum_type` and `factor_type` are the types of the respective bound parameters.        BOOST_CONCEPT_ASSERT((Addable<sum_type>));

       sum = sum + factor * num; // Error because `sum`'s type can't be added :(    } BOOST_LOCAL_FUNCTION_END(add)

   add(100.0);

   return 0; }

Sorry, I forgot to mention... of course, with the new simplified Boost.Local syntax and using C99 variadic macros, the above example will actually become: int main() { pod sum; int factor = 10; void BOOST_LOCAL_FUNCTION_PARAMS(double num, const bind factor, bind& sum) { BOOST_CONCEPT_ASSERT((Addable<sum_type>)); sum = sum + factor * num; } BOOST_LOCAL_FUNCTION_NAME(add) add(100.0); return 0; }

On GCC:

$ g++ -Wall -Werror -I../../.. concepts.00.cpp concepts.00.cpp: In static member function ‘static void main()::boost_local_auxXfunctorXadd::boost_local_auxXbody(main()::boost_local_auxXfunctorXadd&, int, main()::boost_se_capture_t_1_add35&, double)’: concepts.00.cpp:39: error: no match for ‘operator+’ in ‘sum + (#‘float_expr’ not supported by dump_expr#<expression error> * num)’ concepts.00.cpp: In destructor ‘Addable<T>::~Addable() [with T = pod]’: /usr/include/boost/concept/detail/general.hpp:29:   instantiated from ‘static void boost::concept::requirement<Model>::failed() [with Model = Addable<pod>]’ concepts.00.cpp:37:   instantiated from here concepts.00.cpp:22: error: no match for ‘operator+’ in ‘((Addable<pod>*)this)->Addable<pod>::x + ((Addable<pod>*)this)->Addable<pod>::y’

Note: In this specific case even the GCC error without the concept assert (error on line 39) is pretty clear but in general allowing programmer to add concept specifications might lead to better error reporting and a better specification of the local function.

-- Lorenzo