On Tue, Feb 8, 2011 at 9:28 PM, Stephan T. Lavavej <stl@exchange.microsoft.com> wrote:
[Lorenzo Caminiti]
I'm confused because the following code doesn't compile on MSVC but it _does_ compiles fine on GCC... typedef void (func_type)(double num = -1.23); // NO STANDARD?? 1) Is this a bug in GCC which should not accept `= -1.23` in `func_type`?
VC is correct to reject this code. (So does EDG.)
C++03 8.3.6 "Default arguments" [dcl.fct.default]/3: "A default argument expression shall be specified only in the parameter-declaration-clause of a function declaration or in a template-parameter (14.1). If it is specified in a parameter-declaration-clause, it shall not occur within a declarator or abstract-declarator of a parameter-declaration.88)"
Footnote 88: "This means that default arguments cannot appear, for example, in declarations of pointers to functions, references to functions, or typedef declarations."
2) Both, GCC and MSVC accept the parameter name `num` as part of the `func_type` type. Can parameter names be specified in function types?
Yes, that's totally fine, they're just ignored. C++03 8.3.5 "Functions" [dcl.fct]/8: "An identifier can optionally be provided as a parameter name", which applies to typedefs too.
Wow! Thanks a lot for all the standard references -- that's very accurate information! Also, are the function parameter storage classifiers `auto` and `register` part of the function type? Can I manipulate (check, add, and remove) them at compile-time using template metafunctions? The expression `typedef int (f_type)(auto int x, register bool y);` complies on both GCC and MSVC so maybe they are part of the function type... NOTE: This is more of a curiosity because for my application I can manipulate the storage classifiers using preprocessor metaprogramming. In fact, `auto` and `register` are known alphanumeric tokens (i.e., keywords) that always appear at the beginning of the parameter type expression so the following macros can be used to manipulate them: #include <boost/preprocessor.hpp> #include <boost/preprocessor/detail/is_unary.hpp> #define IS_AUTO_auto (1) /* must expand to unary */ #define IS_AUTO(tokens) BOOST_PP_IS_UNARY(BOOST_PP_CAT(IS_AUTO_, tokens)) #define REMOVE_AUTO_STRIP_auto /* must expand to nothing */ #define REMOVE_AUTO_(tokens) BOOST_PP_CAT(REMOVE_AUTO_STRIP_, tokens) #define REMOVE_AUTO(tokens) \ BOOST_PP_IIF(IS_AUTO(tokens), \ REMOVE_AUTO_ \ , \ tokens BOOST_PP_TUPLE_EAT(1) \ )(tokens) #define ADD_AUTO(tokens) \ BOOST_PP_EXPR_IIF(BOOST_PP_NOT(IS_AUTO(tokens)), auto) tokens IS_AUTO(auto int x) // 1 IS_AUTO(int x) // 0 REMOVE_AUTO(auto int x) // int x REMOVE_AUTO(int x) // int x ADD_AUTO(auto int x) // auto int x ADD_AUTO(int x) // auto int x (These macros work as long as the type expression starts with an alphanumeric token -- if not, I can wrap the type expression using Boost.Local's `BOOST_IDENTITY_TYPE` as in `BOOST_IDENITY_TYPE(::std::string) s`.) -- Lorenzo