Eric Niebler wrote:
Arkadiy Vertleyb wrote:
What is current state of the art on l-value/r-value detection? (I know Eric made some progress in the past by using the "?" operator).
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It's an open question whether it's possible to do this in standard C++. If it's possible, I'd be very interested.
Here's my latest attempt. This works on gcc 3.4.4 (cygwin), but not on VC7.1 or (sadly) Comeau Online. Language lawyers, start your engines! template<typename T> struct probe { operator T (); operator T volatile const &() const; }; template<typename T> probe<T> make_probe(T const &); template<typename T> char is_volatile(T const &); template<typename T> double is_volatile(T const volatile &); #define IS_RVALUE(x) \ (\ sizeof(char) == \ sizeof(is_volatile(true?make_probe(x):(x)))\ ) // tests struct foo { foo() {} }; foo const make_foo() { return foo(); } int main() { int i; foo const f1; foo f2; char t1[!IS_RVALUE(f1)]; char t2[!IS_RVALUE(f2)]; char t3[IS_RVALUE(foo())]; char t4[IS_RVALUE(make_foo())]; char t5[!IS_RVALUE(i)]; char t6[IS_RVALUE(1)]; return 0; } -- Eric Niebler Boost Consulting www.boost-consulting.com