On Thu, Feb 17, 2011 at 5:13 PM, Edward Diener <eldiener@tropicsoft.com> wrote:
I am requesting that my library, the Variadic Macro Data library, which is in the sandbox in the variadic_macro_data directory, be reviewed for inclusion into Boost.
The variadic_macro_data library adds support and functionality for variadic macros to Boost as well as integrating variadic macros with the Boost PP library without changing the latter library in any way.
I believe others have used my library, can attest to its quality and that it does what it is supposed to do. and have found it useful when using variadic macros with Boost PP. I myself have used its functionality in my own TTI library in the sandbox. Support for variadic macros is implemented in nearly all modern C++ compilers and the syntax is natural for an end-user. The library is finalized as far as functionality is concerned and I would like to see it in Boost and am willing to maintain it as a Boost library.
Is it possible to use variadic macros to detect empty parameters? For example: #include <boost/variadic_macro_data/VariadicMacroData.hpp> // Proposed lib. VMD_DATA_SIZE(1, 2) // 2 VMD_DATA_SIZE(1) // 1 VMD_DATA_SIZE() // 1 not 0 :(( But I would like to the last size to expand to 0 (or have a different macro that would expand to 0 in that case). With a real C99 preprocessor (e.g., GCC) I can do the following because empty macro parameters are supported: #include <boost/variadic_macro_data/VariadicMacroData.hpp> // Proposed lib. #include <boost/preprocessor.hpp> #include <boost/preprocessor/facilities/is_empty.hpp> #define PP_VA_EAT(...) /* must expand to nothing */ #define PP_VA_SIZE_1OR0_(x) BOOST_PP_IIF(BOOST_PP_IS_EMPTY(x), 0, 1) #define PP_VA_SIZE_(size, ...) \ BOOST_PP_IIF(BOOST_PP_EQUAL(size, 1), \ PP_VA_SIZE_1OR0_ \ , \ size PP_VA_EAT \ )(__VA_ARGS__) #define PP_VA_SIZE(...) PP_VA_SIZE_(VMD_DATA_SIZE(__VA_ARGS__), __VA_ARGS__) PP_VA_SIZE(1, 2) // 2 PP_VA_SIZE(1) // 1 PP_VA_SIZE() // 0 :)) But this does not compile on MSVC because while it supports variadics it does not support empty macro parameters :( BTW, a few minor comments on you library: 1) I think a name like BOOST_PP_VA_... is better than BOOST_VMD. "VA" is the same abbreviation for variadics that C99 uses in __VA_ARGS__ and Boost.Preprocessor already uses abbreviations like in BOOST_PP_SEQ. Alternatively, I would consider BOOST_PP_VARIADICS_... but still not "VMD" because programmers will not know what VMD stands for. 2) I would add PP_VA_EAT, PP_VA_IDENTITY, PP_VA_CAT (similar to what they do already in Boost.Preprocessor and they should be trivial to implement). Also, I would add `#define PP_VA_SAME(...) __VA_ARGS__`. Thanks. -- Lorenzo