A solution to the X/Y problem is to use parentheses instead of quotation marks:
define_function( (typename T, typename U) , mi_binary_function , (T, U) );
// yields:
template< typename T, typename U > struct mi_binary_function_impl; template< typename T, typename U > using mi_binary_function = typename mi_binary_function_impl < T, U >::type;
can be implemented as:
#define strip_parens(...) __VA_ARGS__
#define define_function( template_args , function_name , function_args ) \
template< strip_parens template_args > \
struct function_name##_impl; \
\
template< strip_parens template_args > \
using function_name = typename function_name##_impl \
< strip_parens function_args >::type // end
But we can also generate the parameter names automatically (you give them new names in specializations anyway):
define_function(foo, (class, int, typename));
// yields:
template< class T0, int T1, typename T2 > struct foo_impl; template< class T0, int T1, typename T2 > using foo = typename foo_impl < T0, T1, T2 > :: result;
can be implemented as:
#define gen_single_param_name(number_plus_2) \
BOOST_PP_CAT(T, BOOST_PP_DEC(BOOST_PP_DEC(number_plus_2))) // end
#define gen_single_param(s, data, elem) elem gen_single_param_name(s)
#define gen_params_from_seq(seq) BOOST_PP_SEQ_TRANSFORM(gen_single_param, _, seq)
#define gen_single_arg(s, data, elem) gen_single_param_name(s)
#define gen_args_from_seq(seq) BOOST_PP_SEQ_TRANSFORM(gen_single_arg, _, seq)
#define define_function_impl(name, param_seq, arg_seq) \
template< BOOST_PP_SEQ_ENUM(param_seq) > \
struct name ## _impl; \
\
template< BOOST_PP_SEQ_ENUM(param_seq) > \
using name = typename name ## _impl \
< BOOST_PP_SEQ_ENUM(arg_seq) > :: result // end
#define define_function_seq(name, param_seq) \
define_function_impl(name, gen_params_from_seq(param_seq), \
gen_args_from_seq(param_seq)) // end
#define define_function(name, param_list) \
define_function_seq(name, BOOST_PP_VARIADIC_TO_SEQ param_list)