On 10/8/2012 6:08 AM, Michel Morin wrote:
This is just a small note related to boost::result_of.
When BOOST_RESULT_OF_USE_DECLTYPE is defined, boost::result_of tries to use decltype-based implementation (regardless of the compiler's decltype support).
Surprisingly, in a C++03 mode, libc++ defines `decltype` using `__typeof__`:
Bug 12488 (WONTFIX): decltype can be used in C++03 with no errors, no warnings http://llvm.org/bugs/show_bug.cgi?id=12488
So, when used with libc++, boost::result_of can be used with BOOST_RESULT_OF_USE_DECLTYPE even in a C++03 mode.
Does __typeof__ have EXACTLY the same semantics as C++11 decltype? Can it get you either the type and lvalue-ness of an expression, or the variable's declared type, with an extra set of parens? If the expression is a function call, does it force the return type to be complete? We're finding very few compilers have robust-enough implementations of decltype to flip the result_of switch. I think it's pretty improbable that a pre-standard hack like __typeof__ would fit the bill. -- Eric Niebler BoostPro Computing http://www.boostpro.com