Creation of multiple macro messages according to the number of arguments
I am trying to call this function multiple times in a repeditive way.
template<class T>
void METADATA_METHODS_IMPL(std::string& metadata, const T &value, const std::string &key)
{
metadata += boost::format("%1%:%2%") % key % value();
}
I wrote the following macro:
#define METADATA_METHODS_IMPL_1(md, v1)\
METADATA_METHODS_IMPL(md, v1, #v1);
#define METADATA_METHODS_IMPL_2(md, v1, v2)\
METADATA_METHODS_IMPL_1(md, v1)\
METADATA_METHODS_IMPL_1(md, v2)
#define METADATA_METHODS_IMPL_3(md, v1, v2, v3)\
METADATA_METHODS_IMPL_2(md, v1, v2)\
METADATA_METHODS_IMPL_1(md, v3)
etc.
I need to call METADATA_METHODS_IMPL_N
, where N
is the number of arguments in__VA_ARGS__
#define METADATA_METHODS(...)\
std::string METADATA_METHODS_IMPL_FUNC()\
{\
std::string metadata;\
BOOST_PP_OVERLOAD(METADATA_METHODS_IMPL_,__VA_ARGS__)(metadata, __VA_ARGS__)\
return metadata;\
}
The code above (c BOOST_PP_OVERLOAD
) gives me an inappropriate result:
class X
{
std::string F1();
std::string F2();
std::string F3();
METADATA_METHODS(F1, F2, F3);
};
The result is
std::string METADATA_METHODS_IMPL_FUNC()
{
std::string metadata;
METADATA_METHODS_IMPL(metadata, F1, F2, F3, "F1", "F2", "F3");
METADATA_METHODS_IMPL(metadata, , "");
METADATA_METHODS_IMPL(metadata, , "");
return metadata;
};
And I want something like this:
std::string METADATA_METHODS_IMPL_FUNC()
{
std::string metadata;
METADATA_METHODS_IMPL(metadata, F1, "F1");
METADATA_METHODS_IMPL(metadata, F2, "F2");
METADATA_METHODS_IMPL(metadata, F3, "F3");
return metadata;
};
- Does anyone know how to achieve the desired result?
- Is it possible to use a library
Boost.preprocessor
to automatically generateMETADATA_METHODS_IMPL_K
for someK in [1 .. 10]
withMETADATA_METHODS_IMPL_1
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Using these macros, we can force the preprocessor to continue rescanning and enable recursive macros.
#define EVAL(...) EVAL3(EVAL3(EVAL3(__VA_ARGS__)))
#define EVAL3(...) EVAL2(EVAL2(EVAL2(__VA_ARGS__)))
#define EVAL2(...) EVAL1(EVAL1(EVAL1(__VA_ARGS__)))
#define EVAL1(...) EVAL0(EVAL0(EVAL0(__VA_ARGS__)))
#define EVAL0(...) __VA_ARGS__
We can define some helper functions for creating concepts.
#define CAT(a, ...) PRIMITIVE_CAT(a,__VA_ARGS__)
#define PRIMITIVE_CAT(a, ...) a ## __VA_ARGS__
#define EMPTY()
#define EAT(...)
#define IDENT(...) __VA_ARGS__
#define DEFER(id) id EMPTY()
#define OBSTRUCT(...) __VA_ARGS__ DEFER(EMPTY)()
#define I_TRUE(t,f) t
#define I_FALSE(t,f) f
#define I_IS_DONE(a,b,...) b
#define TRUE_DONE() ~, I_TRUE
#define IS_DONE(b) OBSTRUCT(I_IS_DONE)(CAT(TRUE_,b)(),I_FALSE)
And create this macro function that wraps the first parameter for each.
#define MM() MM_CALL
#define MM_NEXT(Macro,md,a,...) \
IS_DONE(a)( \
EAT \
, \
OBSTRUCT(MM)() \
) \
(Macro,md,a,__VA_ARGS__)
#define MM_CALL(Macro,md,a,...) \
Macro(md,a) \
MM_NEXT(Macro,md,__VA_ARGS__)
#define MacroMap(Macro,md,...) EVAL(MM_CALL(Macro,md,__VA_ARGS__,DONE))
After defining the implementation-related functions
#define METADATA_METHODS_IMPL_MACRO(md,a) \
METADATA_METHODS_IMPL(md, a, #a);
#define METADATA_METHODS(md,...) \
MacroMap(METADATA_METHODS_IMPL_MACRO,md,__VA_ARGS__) \
return md
It:
METADATA_METHODS(metadata, F1, F2, F3);
Results in this (after adding some formatting):
METADATA_METHODS_IMPL(metadata, F1, "F1");
METADATA_METHODS_IMPL(metadata, F2, "F2");
METADATA_METHODS_IMPL(metadata, F3, "F3");
return metadata;
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