Instantiating templates and classes with a preliminary forcing process
Working with the seemingly standard demonstrations w
, x
, y
, z
, suppose I have the following macro, trying to convert to a preprocessor macro "iterability"
#define INSTANTIATE_FUNC(rtype, func_name, ...) \
template rtype func_name< w > (__VA_ARGS__); \
template rtype func_name< x > (__VA_ARGS__); \
template rtype func_name< y > (__VA_ARGS__); \
template rtype func_name< z > (__VA_ARGS__);
For completeness, let's say we are trying to create the following
struct w { static constexpr int data = 0; };
struct x { static constexpr int data = 1; };
struct y { static constexpr int data = 2; };
struct z { static constexpr int data = 3; };
template <class Data>
void printData(const std::string &prefix) {
std::cout << prefix << Data::data << std::endl;
}
INSTANTIATE_FUNC(void, printData, const std::string &prefix)
I've made minimal sense with the build system for convenience, so that if you're interested in trying, you don't need to recreate everything :)
I can't figure out how to approach this. The only functional (but not useful) hit
#include <boost/preprocessor/list/for_each.hpp>
#define LIST (w, (x, (y, (z, BOOST_PP_NIL))))
#define MACRO(r, data, elem) template void data < elem > (const std::string &prefix);
#define INSTANTIATE_FUNC(rtype, func_name, ...) \
BOOST_PP_LIST_FOR_EACH(MACRO, func_name, LIST)
This works, but clearly doesn't match.
-
Why doesn't this work for sequences as well?#include <boost/preprocessor/seq/for_each.hpp> // this does work, my code included the wrong header // on what I was testing with (seq/for_each_i.hpp) #define SEQ (x)(y)(z)(w) #define INSTANTIATE_FUNC(rtype, func_name, ...) \ BOOST_PP_SEQ_FOR_EACH(MACRO, func_name, SEQ)
-
How do I approach creation
template rtype func_name < {w,x,y,z} > {args,in,__VA_ARGS__}
? I've tried a few different things, but the problem seems to fail, for example, just fetchw
and then walk through__VA_ARGS__
then continue. I am trying to somehow get itBOOST_PP_LIST_FOR_EACH_R
to work. Is that at least the right thing to do? -
As a sanity check, you cannot define a macro in the macro on the right? Something in the spirit
#define INSTANTIATE_FUNC(rtype, func_name, ...) \ #define MACRO_##func_name(r, data, elem) data < elem > (__VA_ARGS__); \ BOOST_PP_LIST_FOR_EACH(MACRO_##func_name, func_name, LIST)
Ultimately I am working towards the goal of including an extra extension LIST
/ SEQ
( SEQ
for which it is much easier) if that means anything. Thanks for any suggestions / resources.
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Your problem seems to be that you need to deliver multiple chunks of data to MACRO
in BOOST_PP_(LIST|SEQ)_FOR_EACH
and you can only use one "slot". What you seem to be missing is that you can group these chunks, for example in a tuple, and then access the various elements within yours MACRO
with BOOST_PP_TUPLE_ELEM
. Something like this might work:
//These are not required, just to help with readability
#define MACRO_GET_RETURN_TYPE(TUPLE) BOOST_PP_TUPLE_ELEM(3,0,TUPLE)
#define MACRO_GET_FUNC_NAME(TUPLE) BOOST_PP_TUPLE_ELEM(3,1,TUPLE)
#define MACRO_GET_ARGS_SEQ(TUPLE) BOOST_PP_TUPLE_ELEM(3,2,TUPLE)
#define MACRO(_, DATA, ELEM) template MACRO_GET_RETURN_TYPE(DATA) MACRO_GET_FUNC_NAME(DATA) < ELEM > (BOOST_PP_SEQ_ENUM(MACRO_GET_ARGS_SEQ(DATA)));
// with boost seq
#define SEQ (x)(y)(z)(w)
#define INSTANTIATE_FUNC(rtype, func_name, ...) \
BOOST_PP_SEQ_FOR_EACH(MACRO, (rtype,func_name,BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)), SEQ)
PS: No, you cannot define a macro inside a macro, and the code you posted here works for sequences, the one in your gist is not associated with the wrong title.
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