On Wed, Apr 13, 2011 at 1:35 PM, Jeffrey Lee Hellrung, Jr. < jeffrey.hellrung@gmail.com> wrote:
That would likely have issues with commas in the conditional, which I don't think "double parens" could fix. That is, it's a problem unless all C++0x compilers which support this use of SFINAE also support variadic templates...
I assume you mean variadic macros not variadic templates? Double parentheses would work fine when the compiler doesn't support variadic macros. Just define the macro as such, or similar: #define BOOST_ENABLE_IF( condition )\ typename ::boost::enable_if\ < typename ::boost::function_traits< void condition >::arg1_type\ , int >::type = 0 In fact it's possible to supply a simple variadic version when available and a regular macro similar to the one above when not, having the same macro name in either case without issue. You'd do this by making the variadic version check if the argument is parenthesized (which is possible with the preprocessor) and simply strip the parentheses if they are there. This allows backward compatibility by allowing people to specify either parenthesized or unparenthesized arguments. Anyway, all of this parentheses hubbub is probably unecessary since as far as I know all compilers that have any experimental C++0x support already also support variadic macros (probably in part because of C99). -- -Matt Calabrese