On Mon, Feb 7, 2011 at 5:29 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
AMDG
On 2/7/2011 1:52 PM, Lorenzo Caminiti wrote:
Too bad I don't think I can actually do this :( (given that `void` can be _any_ token so I cannot strip it out with the pp...). I might be able however to pull the return type outside the macro as in Alex-Steven's syntax:
void BOOST_LOCAL_FUNCTION(int x, double& y, const bind a, // [14] const bind& b, bind& c, bind d) { ... } BOOST_LOCAL_FUNCTION_END(f) f(1, 1.23);
And regardless of what Alex-Steven did, I could do this by expanding to a dummy variable/expression and then get its type with typeof (but the library will then require typeof to determine the result type even when no bound parameter is used and for a type which is specified by programmes as a type -- that'd be strange):
void *result_ptr; // Plus append __LINE__... typedef typeof(*result_ptr) result_type; ...
That's almost what we did.
void deduce_result(); typedef boost::function_traits< typeof(&deduce_result)>::result_type result_type;
is a little better. (It can handle references.)
This code doesn't compile on GCC (but it compiles on MSVC) within function template: #include <boost/typeof/typeof.hpp> #include <boost/type_traits.hpp> template<typename T> void g(T x) { T (deduce_result)(); typedef typename boost::function_traits< // Line 8 BOOST_TYPEOF(deduce_result)>::result_type result_type; struct s { result_type f(T& x) { return x; } // Line 12 } ss; ss.f(x); } void f(int x) { int& (deduce_result)(); typedef boost::function_traits< BOOST_TYPEOF(deduce_result)>::result_type result_type; struct s { result_type f(int& x) { return x; } } ss; ss.f(x); } int main() { g(1); f(1); return 0; } $ g++ -Wall -Werror -I../../.. r00.cpp r00.cpp: In member function ‘typename boost::function_traits<__typeof__ (boost::type_of::ensure_obj(deduce_result))>::result_type g(T)::s::f(T&) [with T = int]’: r00.cpp:14: instantiated from ‘void g(T) [with T = int]’ r00.cpp:29: instantiated from here r00.cpp:12: error: ‘deduce_result’ was not declared in this scope It looks like GCC expands `deduce_result` within the struct on line 12 when typename is used instead of resolving the type at the typedef on line 8... I don't really understand what is going on... any idea? $ g++ --version g++ (GCC) 4.3.4 20090804 (release) 1 Copyright (C) 2008 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Thanks a lot! -- Lorenzo